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.*;
import java.util.*;


public class ForcesC {
	public static class FastReader {
		BufferedReader br;
		StringTokenizer st;
		//it reads the data about the specified point and divide the data about it ,it is quite fast
		//than using direct 

		public FastReader() {
			br = new BufferedReader(new InputStreamReader(System.in));
		}

		String next() {
			while (st == null || !st.hasMoreTokens()) {
				try {
					st = new StringTokenizer(br.readLine());
				} catch (Exception r) {
					r.printStackTrace();
				}
			}
			return st.nextToken();
		}

		int nextInt() {
			return Integer.parseInt(next());//converts string to integer
		}

		double nextDouble() {
			return Double.parseDouble(next());
		}

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

		String nextLine() {
			String str = "";
			try {
				str = br.readLine();
			} catch (Exception r) {
				r.printStackTrace();
			}
			return str;
		}
	}



	public static PrintWriter out = new PrintWriter (new BufferedOutputStream(System.out));
	static long mod = (long)(1e9+7);
	static FastReader sc = new FastReader();
    static List<Integer>[] edge ;
	
	public static void main(String[] args) throws FileNotFoundException {	     
	     
		 int n = sc.nextInt();
		 edge = new ArrayList[n+1];
		 visited = new boolean[n+1];  
		for(int i=0;i<=n;++i) {
			edge[i] = new ArrayList<>();
		}
		for(int v=2;v<=n;++v) {
			int u = sc.nextInt();
		//	int v = sc.nextInt();
				edge[u].add(v);
				edge[v].add(u);
			
		}
		int[] sum = new int[n+1];
		 a = new int[n+1];
		for(int i=1;i<=n;++i) sum[i] = sc.nextInt();
		 found = true;
		dfs(1,0,sum);
		long ans = 0;
		if(found) {
		for(int x : a) ans+=x;
		}else ans = -1;
		out.println(ans);
		
		out.close();
	}
	static boolean[] visited;
	static int[] a;
	static boolean found;
	private static void dfs(int v, int parent,int[] sum) {
		
		if(sum[v] != -1) {
			a[v] = sum[v]-sum[parent];
			
		}else {
			int min = Integer.MAX_VALUE;
			for(int child : edge[v]) {
				if(child != parent) 
					min = Math.min(min, sum[child]-sum[parent]);
			}
			        if(min == Integer.MAX_VALUE) min = 0;
					a[v] = min;
					sum[v] = a[v]+sum[parent];	
		}
		if(a[v]<0) {
			found = false;
			return;
		}
		
		//out.println(v+" : "+sum[v]+" "+a[v]);
	
	
		for(int child : edge[v]) {
			if(child != parent) 
				dfs(child,v,sum);
		}
	}
}