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.util.InputMismatchException;
import java.io.IOException;
import java.util.ArrayList;
import java.io.InputStream;

/**
 * Built using CHelper plug-in
 * Actual solution is at the top
 *
 * @author real
 */
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);
        treecf530 solver = new treecf530();
        solver.solve(1, in, out);
        out.close();
    }

    static class treecf530 {
        ArrayList<ArrayList<Integer>> list;
        long[] cost;
        long[] val;

        public void solve(int testNumber, InputReader in, PrintWriter out) {
            int n = in.nextInt();
            list = in.initlist(n);
            val = new long[n + 1];
            for (int i = 2; i <= n; i++) {
                int p = in.nextInt();
                list.get(i).add(p);
                list.get(p).add(i);
            }
            cost = new long[n + 1];
            for (int i = 1; i <= n; i++) {
                cost[i] = in.nextInt();
            }
            long ans = 0;
            dfs(1, 0, 0);
            for (int i = 0; i <= n; i++) {
                if (val[i] < 0) {
                    out.print(-1);
                    return;
                }
                ans += val[i];
            }
            out.print(ans);
        }

        void dfs(int n, int p, long sum) {
            if (cost[n] == -1) {
                long min = Integer.MAX_VALUE;
                for (int x : list.get(n)) {
                    if (x != p) {
                        min = Math.min(min, cost[x]);
                    }
                }
                if (min == Integer.MAX_VALUE) {
                    val[n] = 0;
                    return;
                } else {
                    long va = min - sum;
                    val[n] = va;
                }
                for (int x : list.get(n)) {
                    if (x != p) {
                        dfs(x, n, min);
                    }
                }
            } else {
                val[n] = cost[n] - sum;
                for (int x : list.get(n)) {
                    if (x != p) {
                        dfs(x, n, cost[n]);
                    }
                }
            }

        }

    }

    static class InputReader {
        private final InputStream stream;
        private final byte[] buf = new byte[8192];
        private int curChar;
        private int snumChars;

        public InputReader(InputStream st) {
            this.stream = st;
        }

        public int read() {
            //*-*------clare------
//remeber while comparing 2 non primitive data type not to use ==
//remember Arrays.sort for primitive data has worst time case complexity of 0(n^2) bcoz it uses quick sort
//again silly mistakes ,yr kb tk krta rhega ye mistakes
//try to write simple codes ,break it into simple things
            // for test cases make sure println(); ;)
//knowledge>rating
        /*
        public class Main
        implements Runnable{
    public static void main(String[] args) {
        new Thread(null,new Main(),"Main",1<<26).start();

    }
    public void run() {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        InputReader in = new InputReader(inputStream);
        PrintWriter out = new PrintWriter(outputStream);
        TaskC solver = new TaskC();//chenge the name of task
        solver.solve(1, in, out);
        out.close();
    }
         */

            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 = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            int res = 0;
            do {
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public ArrayList<ArrayList<Integer>> initlist(int n) {
            ArrayList<ArrayList<Integer>> list = new ArrayList<>();
            for (int i = 0; i <= n; i++) {
                list.add(new ArrayList<Integer>());
            }
            return list;
        }

        public boolean isSpaceChar(int c) {
            return c == ' ' || c == '\n' || c == '\r' || c == '\t' || c == -1;
        }

    }
}

