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.awt.*;
import java.io.OutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.io.Closeable;
import java.io.Writer;
import java.io.OutputStreamWriter;
import java.lang.reflect.Array;
import java.util.Arrays;

public class water {
    public static long sum=0;
    public static boolean ok=true;
        public static int  dps(int a[][],int sx[],int x,int poi){
            int add=-1;
            if(sx[poi]!=-1&&sx[poi]<x){
                ok=false;
            }
            else if(sx[poi]>=x){
                add=sx[poi]-x;
                sum+=add;
                x=sx[poi];
            }

            if(a[poi].length==1){

            }
            else{
                int add2=-1;
                int lon=a[poi].length-2;
                for(int i=1;i<a[poi].length;i++){
                    int add3=dps(a,sx,x,a[poi][i]);
                    if(add3==-1){
                        lon--;
                    }
                    else if(add2==-1){
                        add2=add3;
                    }
                    else if(add3<add2)
                        add2=add3;
                }
                if(add2>=0&&add==-1){
                    //System.out.println("lon"+lon);
                    sum-=add2*(lon);
                    add=add2;
                }


            }
            return add;

        }
    public static void main(String[] args) {
        InputStream inputStream = System.in;
        OutputStream outputStream = System.out;
        FastInput input = new FastInput(inputStream);
        FastOutput out = new FastOutput(outputStream);
        int n = input.scanInt();
        int a[][]=new int [n+1][];
        int x[]=new int [n];
        int len[]=new int[n+1];
        int sx[]=new int [n+1];
        for(int i=1;i<n;i++){
            x[i]= input.scanInt();
            len[x[i]]++;
        }

        for(int i=1;i<n+1;i++){
            a[i]=new int[len[i]+1];
        }
        for(int i=1;i<n;i++){
             a[x[i]][len[x[i]]--]=i+1;
        }
        for(int i=1;i<n+1;i++){
            sx[i]= input.scanInt();
        }
        dps(a,sx,0,1);
        if(ok)        System.out.println(sum);
        else
            System.out.println("-1");
        out.close();
    }

    static class FastInput {
        private final InputStream is;
        private StringBuilder defaultStringBuf = new StringBuilder(1 << 13);
        private byte[] buf = new byte[1 << 13];
        private int bufLen;
        private int bufOffset;
        private int next;
        public FastInput(InputStream is) {
            this.is = is;
        }
        private int read() {
            while (bufLen == bufOffset) {
                bufOffset = 0;
                try {
                    bufLen = is.read(buf);
                } catch (IOException e) {
                    bufLen = -1;
                }
                if (bufLen == -1) {
                    return -1;
                }
            }
            return buf[bufOffset++];
        }
        public void skipBlank() {
            while (next >= 0 && next <= 32) {
                next = read();
            }
        }
        public String next() {
            return readString();
        }
        public int scanInt() {
            int sign = 1;
            skipBlank();
            if (next == '+' || next == '-') {
                sign = next == '+' ? 1 : -1;
                next = read();
            }
            int val = 0;
            while (next >= '0' && next <= '9') {
                val = val * 10 + next - '0';
                next = read();
            }
            return (sign*val);
        }

        public String readString(StringBuilder builder) {
            skipBlank();
            while (next > 32) {
                builder.append((char) next);
                next = read();
            }
            return builder.toString();
        }

        public String readString() {
            defaultStringBuf.setLength(0);
            return readString(defaultStringBuf);
        }

    }
    static class FastOutput implements AutoCloseable, Closeable, Appendable {
        private StringBuilder cache = new StringBuilder(1 << 20);
        private final Writer os;

        public FastOutput append(CharSequence csq) {
            cache.append(csq);
            return this;
        }

        public FastOutput append(CharSequence csq, int start, int end) {
            cache.append(csq, start, end);
            return this;
        }

        public FastOutput(Writer os) {
            this.os = os;
        }

        public FastOutput(OutputStream os) {
            this(new OutputStreamWriter(os));
        }

        public FastOutput append(char c) {
            cache.append(c);
            return this;
        }

        public FastOutput append(String c) {
            cache.append(c);
            return this;
        }
        public FastOutput append(int c) {
            cache.append(c);
            return this;
        }
        public FastOutput println(int c) {
            return append(c).println();
        }
        public FastOutput println(String c) {
            return append(c).println();
        }

        public FastOutput println() {
            //cache.append(System.lineSeparator());
            return this;
        }

        public FastOutput flush() {
            try {
                os.append(cache);
                os.flush();
                cache.setLength(0);
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
            return this;
        }

        public void close() {
            flush();
            try {
                os.close();
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }

        public String toString() {
            return cache.toString();
        }

    }


}


