Mitya has a rooted tree with n vertices indexed from 1 to n, where the root has index 1. Each vertex v initially had an integer number a_v ≥ 0 written on it. For every vertex v Mitya has computed s_v: the sum of all values written on the vertices on the path from vertex v to the root, as well as h_v — the depth of vertex v, which denotes the number of vertices on the path from vertex v to the root. Clearly, s_1=a_1 and h_1=1.

Then Mitya erased all numbers a_v, and by accident he also erased all values s_v for vertices with even depth (vertices with even h_v). Your task is to restore the values a_v for every vertex, or determine that Mitya made a mistake. In case there are multiple ways to restore the values, you're required to find one which minimizes the total sum of values a_v for all vertices in the tree.

Input

The first line contains one integer n — the number of vertices in the tree (2 ≤ n ≤ 10^5). The following line contains integers p_2, p_3, ... p_n, where p_i stands for the parent of vertex with index i in the tree (1 ≤ p_i < i). The last line contains integer values s_1, s_2, ..., s_n (-1 ≤ s_v ≤ 10^9), where erased values are replaced by -1.

Output

Output one integer — the minimum total sum of all values a_v in the original tree, or -1 if such tree does not exist.

Examples

Input


5
1 1 1 1
1 -1 -1 -1 -1


Output


1


Input


5
1 2 3 1
1 -1 2 -1 -1


Output


2


Input


3
1 2
2 -1 1


Output


-1
//package math_codet;

import java.io.*;
import java.util.*;

public class lets_do {
    InputReader in;
    PrintWriter out;
    Helper_class h;
    final long mod = 1000000007;
    public static void main(String[] args) throws java.lang.Exception{
        new lets_do().run();
    }
    void run() throws Exception{
        in=new InputReader(System.in);
        out = new PrintWriter(System.out);
        h = new Helper_class();
        int t = 1;
        while(t-->0)
            solve();
        out.flush();
        out.close();
    }
    ArrayList<Integer>[] tree;
    int[] height;
    long[] val;
    long[] val1;
    long[] max;
    int[] par;
    void dfs1(int v, int e, int h){
        height[v] = h;
        par[v] = e;
        if(h % 2 == 0)
            val[v] = val[par[v]];
        for(Integer u : tree[v]){
            if(u != e)
                dfs1(u, v, h + 1);
        }
    }
    boolean ok = false;
    void dfs2(int v, int e, long sum){
        if(height[v] % 2 == 0){
            long min = Integer.MAX_VALUE;
            for(Integer u : tree[v]){
                if(u != e)
                    min = Math.min(min, val[u]);
            }
            if(min == Integer.MAX_VALUE)
                val1[v] = 0;
            else
                val1[v] = min - sum;
            for(Integer u : tree[v]){
                if(u != e)
                    dfs2(u, v, min);
            }
        }
        else{
            val1[v] = val[v] - sum;
            for(Integer u : tree[v]){
                if(u != e)
                    dfs2(u, v, val[v]);
            }
        }
    }
    void solve(){
        int n = h.ni();
        tree = new ArrayList[n];
        height = new int[n];
        val = new long[n];
        par = new int[n];
        val1 = new long[n];
        max = new long[n];

        int i = 0;
        Arrays.fill(val1, -1);
        for(i = 0; i < n; i++)
            tree[i] = new ArrayList<Integer>();
        for(i = 1; i < n; i++){
            int x = h.ni() - 1;
            tree[i].add(x);
            tree[x].add(i);
        }
        for(i = 0; i < n; i++){
            val[i] = h.nl();
            if(val[i] == -1)
                val[i] = 0;
        }
        max[0] = val[0];
        dfs1(0, -1, 1);
        dfs2(0, -1, 0);
        long sum = 0;
        for(i = 0; i < n; i++){
            if(val1[i] < 0){
                h.pn(-1);
                return;
            }
            sum += val1[i];
        }
        h.pn(sum);
    }

    static final Comparator<Pair> com=new Comparator<Pair>(){
        public int compare(Pair a, Pair b){
            if(Integer.compare(a.x, b.x) != 0)
                return Integer.compare(a.x, b.x);
            else
                return Integer.compare(a.y, b.y);
        }
    };


    class Pair{
        int x;
        int y;
        Pair(int p, int q){
            x = p;
            y = q;
        }
    }

    class Edge{
        int u , v, ind;
        boolean is_bridge;
        Edge(int a, int b, int i){
            u = a;
            v = b;
            ind = i;
        }
        int other(int x) {
            return u ^ v ^ x;
        }
    }

    class Helper_class{
        long gcd(long a, long b){return (b==0)?a:gcd(b,a%b);}
        int gcd(int a, int b){return (b==0)?a:gcd(b,a%b);}
        int bitcount(long n){return (n==0)?0:(1+bitcount(n&(n-1)));}
        void p(Object o){out.print(o);}
        void pn(Object o){out.println(o);}
        void pni(Object o){out.println(o);out.flush();}
        String n(){return in.next();}
        String nln(){return in.nextLine();}
        int ni(){return Integer.parseInt(in.next());}
        long nl(){return Long.parseLong(in.next());}
        double nd(){return Double.parseDouble(in.next());}

        long mul(long a,long b){
            if(a>=mod)a%=mod;
            if(b>=mod)b%=mod;
            a*=b;
            if(a>=mod)a%=mod;
            return a;
        }
        long modPow(long a, long p){
            long o = 1;
            while(p>0){
                if((p&1)==1)o = mul(o,a);
                a = mul(a,a);
                p>>=1;
            }
            return o;
        }
        long add(long a, long b){
            if(a>=mod)a%=mod;
            if(b>=mod)b%=mod;
            if(b<0)b+=mod;
            a+=b;
            if(a>=mod)a-=mod;
            return a;
        }
    }

    class InputReader{
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
 
        public InputReader(InputStream stream) {
            this.stream = stream;
        }
 
        public int read() {
            if (numChars == -1)
                throw new UnknownError();
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new UnknownError();
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar++];
        }
 
        public int peek() {
            if (numChars == -1)
                return -1;
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    return -1;
                }
                if (numChars <= 0)
                    return -1;
            }
            return buf[curChar];
        }
 
        public void skip(int x) {
            while (x-- > 0)
                read();
        }
 
        public int nextInt() {
            return Integer.parseInt(next());
        }
 
        public long nextLong() {
            return Long.parseLong(next());
        }
 
        public String nextString() {
            return next();
        }
 
        public String next() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            StringBuffer res = new StringBuffer();
            do {
                res.appendCodePoint(c);
                c = read();
            } while (!isSpaceChar(c));
 
            return res.toString();
        }
 
        public String nextLine() {
            StringBuffer buf = new StringBuffer();
            int c = read();
            while (c != '\n' && c != -1) {
                if (c != '\r')
                    buf.appendCodePoint(c);
                c = read();
            }
            return buf.toString();
        }
 
        public double nextDouble() {
            int c = read();
            while (isSpaceChar(c))
                c = read();
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            double res = 0;
            while (!isSpaceChar(c) && c != '.') {
                if (c == 'e' || c == 'E')
                    return res * Math.pow(10, nextInt());
                if (c < '0' || c > '9')
                    throw new InputMismatchException();
                res *= 10;
                res += c - '0';
                c = read();
            }
            if (c == '.') {
                c = read();
                double m = 1;
                while (!isSpaceChar(c)) {
                    if (c == 'e' || c == 'E')
                        return res * Math.pow(10, nextInt());
                    if (c < '0' || c > '9')
                        throw new InputMismatchException();
                    m /= 10;
                    res += (c - '0') * m;
                    c = read();
                }
            }
            return res * sgn;
        }
 
        public boolean hasNext() {
            int value;
            while (isSpaceChar(value = peek()) && value != -1)
                read();
            return value != -1;
        }
 
        private boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }
    }
}