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
import java.util.*;
import java.io.*;
//import javafx.util.Pair;
public class Main implements Runnable 
{  
    
    static class Pair implements Comparable <Pair>
    {
        int x;
        long wt;
        Pair(int x,long wt)
        {
            this.x=x;
            this.wt=wt;
        }
        public int compareTo(Pair p)
        {
            return Long.compare(wt,p.wt);
        }
    }
    
    public static void main(String[] args)
    {
        new Thread(null, new Main(), "rev", 1 << 29).start();
    }

    public void run()
    {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        Task solver = new Task();
        solver.solve(1,in,out);
        out.close();
    }
    
    static class Task
    { 
        ArrayList <Integer>[]adj;  
        int a[],sum[];
        
        boolean dfs(int s,int p)
        {
            if(s!=1 && adj[s].size()==1)
                if(sum[s]==-1)
                    return true;
                    
            int sump=sum[p],min=Integer.MAX_VALUE;
            if(sum[s]==-1)
            {
                for(int i:adj[s])
                {
                    if(i==p)
                        continue;
                    min=Math.min(min,sum[i]);
                }
                if(min<sum[p])
                    return false;
                sum[s]=min;
                a[s]=sum[s]-sum[p];
                for(int i:adj[s])
                {
                    if(i==p)
                        continue;
                    a[i]=sum[i]-sum[s];
                    if(!dfs(i,s))
                        return false;
                }
            }
            else
            {
                for(int i:adj[s])
                {
                    if(i==p)
                        continue;
                    if(!dfs(i,s))
                        return false;
                }
            }
            return true;
        }
        
        void solve(int testNumber, InputReader in, PrintWriter out)
        {
            int n=in.nextInt(),x;
            adj=new ArrayList[n+1];
            for(int i=1;i<=n;i++)
                adj[i]=new ArrayList<>();
            a=new int[n+1];
            for(int i=2;i<=n;i++)
            {
                x=in.nextInt();
                adj[i].add(x);
                adj[x].add(i);
            }
            sum=in.nextIntArray(n+1);
            a[1]=sum[1];
            if(!dfs(1,0))
                out.println("-1");
            else
            {
                long ans=0;
                for(int i=1;i<=n;i++)
                    ans+=a[i];
                out.println(ans);
            }
        }
    }
    /*static class OutputWriter
    {
        private final PrintWriter writer;

        public OutputWriter(OutputStream outputStream)
        {
            writer = new PrintWriter(new BufferedWriter(new OutputStreamWriter(outputStream)));
        }

        public OutputWriter(Writer writer)
        {
            this.writer = new PrintWriter(writer);
        }

        public void print(Object... objects)
        {
            for(int i=0;i<objects.length;i++)
            {
                if (i!=0)
                {
                    writer.print(' ');
                }
                writer.print(objects[i]);
            }
        }

        public void println(Object... objects)
        {
            print(objects);
            writer.println();
        }

        public void close()
        {
            writer.close();
        }
    }*/

static class InputReader 
{
    private InputStream stream;
    private byte[] buf = new byte[8192];
    private int curChar, snumChars;
    private SpaceCharFilter filter;
 
    public InputReader(InputStream stream) 
    {
        this.stream = stream;
    }
 
    public int snext() 
    {
        if(snumChars==-1)
            throw new InputMismatchException();
        if(curChar>=snumChars)
        {
            curChar=0;
            try 
            {
                snumChars = stream.read(buf);                
            } 
            catch(IOException e) 
            {
                throw new InputMismatchException();
            }
            if(snumChars<=0)
                return -1;
        }
        return buf[curChar++];
    }
 
    public int nextInt()
    {
        int c = snext();
        while(isSpaceChar(c))
            c=snext();
        int sgn=1;
        if(c=='-')
        {
            sgn = -1;
            c = snext();
        }
        int res=0;
        do
        {
            if(c<'0' || c>'9')
                throw new InputMismatchException();
            res*=10;
            res+=c-'0';
            c=snext();
            }while(!isSpaceChar(c));
        return res * sgn;
    }
 
    public long nextLong()
    {
        int c = snext();
        while(isSpaceChar(c))
            c=snext();
        int sgn=1;
        if(c=='-')
        {
            sgn=-1;
            c=snext();
        }
        long res=0;
        do{
            if (c<'0' || c>'9')
                throw new InputMismatchException();
            res*=10;
            res+=c-'0';
            c=snext();
        }while (!isSpaceChar(c));
        return res * sgn;
    }
 
    public int[] nextIntArray(int n)
    {
        int a[]=new int[n];
        for(int i=1; i<n; i++)
            a[i]=nextInt();
        return a;
    }

    public long[] nextLongArray(int n)
    {
        long a[]=new long[n];
        for(int i=1; i<n; i++)
            a[i]=nextLong();
        return a;
    }
    public String nextString()
    {
        int c=snext();
        while(isSpaceChar(c))
            c=snext();
        StringBuilder res=new StringBuilder();
        do{
            res.appendCodePoint(c);
            c = snext();
        }while (!isSpaceChar(c));
        return res.toString();
    }
 
    public boolean isSpaceChar(int c)
    {
        if(filter != null)
            return filter.isSpaceChar(c);
        return c==' ' || c=='\n' || c=='\r' || c=='\t' || c==-1;
    }
 
    public interface SpaceCharFilter
    {
        public boolean isSpaceChar(int ch);
    }
}
}