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.OutputStream;
import java.io.PrintWriter;
import java.util.List;
import java.io.BufferedWriter;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.util.InputMismatchException;
import java.io.IOException;
import java.util.Comparator;
import java.io.InputStream;
import java.util.ArrayList;

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

    static class DSumInTheTree {
        List[] g;
        long[] s;
        long ans;
        boolean isp = true;

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

            g = new List[n];

            in.readTree(g, n, 1);

            s = in.nextLongArray(n);

            dfs(0, -1, 0);

            if (!isp) {
                out.println(-1);
                return;
            }

            out.println(ans);
        }

        void dfs(int u, int p, int ch) {
            if (u != 0) {
                if (g[u].size() == 1) {
                    if (ch % 2 == 0) {
                        ans += s[u] - s[p];
                    }
                    return;
                }
            }

            if (ch % 2 == 0) {
                ans += s[u];

                if (p != -1) {
                    ans -= s[p];
                }

                for (int i = 0; i < g[u].size(); i++) {
                    int v = (int) g[u].get(i);

                    if (v != p) {
                        dfs(v, u, ch + 1);
                    }
                }
            } else {
                long min = s[p];

                List<Long> l = new ArrayList<>();

                for (int i = 0; i < g[u].size(); i++) {
                    int v = (int) g[u].get(i);

                    if (v != p) {
                        //dfs(v, u, ch + 1);
                        l.add(s[v]);
                    }
                }

                l.sort(Comparator.naturalOrder());

                long max = l.get(0);

                if (min > max) {
                    isp = false;
                    return;
                }

                s[u] = max;

                ans += max - s[p];

                for (int i = 0; i < g[u].size(); i++) {
                    int v = (int) g[u].get(i);

                    if (v != p) {
                        dfs(v, u, ch + 1);
                    }
                }
            }
        }

    }

    static class InputReader {
        private InputStream stream;
        private byte[] buf = new byte[1024];
        private int curChar;
        private int numChars;
        private InputReader.SpaceCharFilter filter;

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

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

        public int read() {
            if (numChars == -1) {
                throw new InputMismatchException();
            }
            if (curChar >= numChars) {
                curChar = 0;
                try {
                    numChars = stream.read(buf);
                } catch (IOException e) {
                    throw new InputMismatchException();
                }
                if (numChars <= 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 {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public long nextLong() {
            int c = read();
            while (isSpaceChar(c)) {
                c = read();
            }
            int sgn = 1;
            if (c == '-') {
                sgn = -1;
                c = read();
            }
            long res = 0;
            do {
                if (c < '0' || c > '9') {
                    throw new InputMismatchException();
                }
                res *= 10;
                res += c - '0';
                c = read();
            } while (!isSpaceChar(c));
            return res * sgn;
        }

        public boolean isSpaceChar(int c) {
            if (filter != null) {
                return filter.isSpaceChar(c);
            }
            return isWhitespace(c);
        }

        public long[] nextLongArray(int n) {
            long[] array = new long[n];
            for (int i = 0; i < n; ++i) array[i] = nextLong();
            return array;
        }

        public void readTree(List[] g, int numOfVertices, int offset) {
            int numOfEdges = numOfVertices - 1;

            for (int i = 0; i < numOfVertices; i++) {
                g[i] = new ArrayList();
            }

            for (int i = 0; i < numOfEdges; i++) {
                int p = nextInt() - offset;

                g[p].add(i + 1);
                g[i + 1].add(p);
            }
        }

        public interface SpaceCharFilter {
            public boolean isSpaceChar(int ch);

        }

    }

    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 close() {
            writer.close();
        }

        public void println(long i) {
            writer.println(i);
        }

        public void println(int i) {
            writer.println(i);
        }

    }
}

