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.ArrayList;
import java.util.StringTokenizer;
import java.io.IOException;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.InputStream;

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

    static class Task {
    	public int dfs1(int u,ArrayList<Integer>[] edge,int[] s) {
    		int temp=Integer.MAX_VALUE;
    
    		for(int v:edge[u]) {
    			temp=Math.min(temp,dfs1(v,edge,s));
    		}
    		if(s[u]!=-1)
    			return s[u];
    		if(temp!=Integer.MAX_VALUE)
    			s[u]=temp;
    		return temp;
    	}
    	
    	public void dfs2(int u,ArrayList<Integer>[] edge,int[] s,int[] fa,int[] a) {
    		if(edge[u].size()==0) {
    			if(s[u]==-1)
    				a[u]=0;
    			else
    				a[u]=s[u]-s[fa[u]];
    			return ;
    		}
    		if(u==0)
    			a[u]=s[u];
    		else
    			a[u]=s[u]-s[fa[u]];
    		for(int v:edge[u])
    			dfs2(v,edge,s,fa,a);
    		
    	}
    	
        public void solve(int testNumber, InputReader sc, PrintWriter out) {
        	int n=sc.nextInt();
        	int[] fa=new int[n];
        	ArrayList<Integer>[] edge=new ArrayList[n];
        	for(int i=0;i<n;i++)
        		edge[i]=new ArrayList<Integer>();
        	for(int i=1;i<n;i++) {
        		int p=sc.nextInt()-1;
        		fa[i]=p;
        		edge[p].add(i);
        	}
        	int[] s=new int[n];
        	for(int i=0;i<n;i++)
        		s[i]=sc.nextInt();
        	int[] a=new int[n];
        	dfs1(0,edge,s);
        	dfs2(0,edge,s,fa,a);
        	long ans=0;
        	for(int v:a) {
        		if(v<0) {
        			out.println("-1");
        			return ;
        		}
        		ans+=v;
        	}
        	out.println(ans);
        }
    }

    static class InputReader {
        public BufferedReader reader;
        public StringTokenizer tokenizer;

        public InputReader(InputStream stream) {
            reader = new BufferedReader(new InputStreamReader(stream), 32768);
            tokenizer = null;
        }

        public String next() {
            while (tokenizer == null || !tokenizer.hasMoreTokens()) {
                try {
                    tokenizer = new StringTokenizer(reader.readLine());
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            }
            return tokenizer.nextToken();
        }

        public int nextInt() {
            return Integer.parseInt(next());
        }

        public long nextLong() {
            return Long.parseLong(next());
        }

    }
}
