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.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.DataInputStream;
import java.util.Vector;
import java.io.IOException;
import java.util.InputMismatchException;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author xwchen
 */
public class Main {
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskD solver = new TaskD();
        solver.solve(1, in, out);
        out.close();
    }

    static class TaskD {
        boolean OK = true;

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();

            Vector<Integer>[] adj = new Vector[n];
            for (int i = 0; i < n; ++i) {
                adj[i] = new Vector<>();
            }
            long[] s = new long[n];
            long[] a = new long[n];
            int[] fa = new int[n];
            for (int i = 1; i < n; ++i) {
                fa[i] = in.nextInt() - 1;
                adj[fa[i]].add(i);
            }
            for (int i = 0; i < n; ++i) {
                s[i] = in.nextInt();
            }
            a[0] = s[0];
            dfs(0, 0, 0, adj, s, a, 1);
            if (OK) {
                long sum = 0;
                for (int i = 0; i < n; ++i) {
                    sum += a[i];
                    //out.println(String.format("a[%d] = %d", i, a[i]));
                }
                out.println(sum);
            } else {
                out.println(-1);
            }
        }

        void dfs(int gfa, int fa, int cur, Vector<Integer>[] adj, long[] s, long[] a, int depth) {
            int scnt = 0;
            long mn = 10000000000L;
            for (int i = 0; i < adj[cur].size(); ++i) {
                int son = adj[cur].get(i);
                if (son != fa) {
                    ++scnt;
                    mn = Math.min(mn, s[son]);
                    dfs(fa, cur, son, adj, s, a, depth + 1);
                }
            }
            if (depth % 2 == 0) {
                if (scnt == 0) {
                    a[cur] = 0;
                } else {
                    if (mn < s[fa]) {
                        OK = false;
                    } else {
                        a[cur] = mn - s[fa];
                        for (int i = 0; i < adj[cur].size(); ++i) {
                            int son = adj[cur].get(i);
                            if (son != fa) {
                                a[son] = s[son] - s[fa] - a[cur];
                            }
                        }
                    }
                }
            }
        }

    }

    static class InputReader {
        final private int BUFFER_SIZE = 1 << 10;
        private DataInputStream in;
        private byte[] buffer;
        private int bufferPointer;
        private int bytesRead;

        public InputReader(InputStream inputStream) {
            this.in = new DataInputStream(inputStream);
            buffer = new byte[BUFFER_SIZE];
            bufferPointer = bytesRead = 0;
        }

        public int nextInt() {
            int ret = 0;
            byte c = read();
            while (c <= ' ')
                c = read();
            boolean neg = (c == '-');
            if (neg)
                c = read();
            do {
                ret = ret * 10 + c - '0';
            } while ((c = read()) >= '0' && c <= '9');

            if (neg)
                return -ret;
            return ret;
        }

        private void fillBuffer() {
            try {
                bytesRead = in.read(buffer, bufferPointer = 0, BUFFER_SIZE);
                if (bytesRead == -1)
                    buffer[0] = -1;
            } catch (IOException e) {
                throw new InputMismatchException();
            }
        }

        private byte read() {
            if (bufferPointer == bytesRead)
                fillBuffer();
            return buffer[bufferPointer++];
        }

    }
}

