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.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.HashSet;
import java.util.LinkedList;
import java.util.StringTokenizer;

public class Round530D {

	public static class pair{
		int pos;
		int value;
		
		public pair(int pos,int value) {
			this.pos=pos;
			this.value=value;
		}
	}
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		out=new PrintWriter (new BufferedOutputStream(System.out));
		FastReader s=new FastReader();
		int n=s.nextInt();
		LinkedList<Integer>[] tree=new LinkedList[n];
		for(int i=0;i<n;i++) {
			tree[i]=new LinkedList<Integer>();
		}
		for(int i=1;i<n;i++) {
			int x=s.nextInt();
			tree[x-1].add(i);
		}
		int[] arr=new int[n];
		for(int i=0;i<n;i++) {
			arr[i]=s.nextInt();
		}
		int[] ans=new int[n];
		LinkedList<Integer> queue=new LinkedList<Integer>();
		queue.add(0);
		while(!queue.isEmpty()) {
			int current=queue.removeFirst();
			if(arr[current]==-1) {
				int min=Integer.MAX_VALUE;
				for(Integer x:tree[current]) {
					min=Integer.min(arr[x],min);
				}
				arr[current]=min==Integer.MAX_VALUE?-2:min;
			}
			for(Integer x:tree[current]) {
				queue.addLast(x);
			}
		}
		queue.add(0);
		ans[0]=arr[0];
		while(!queue.isEmpty()) {
			int current=queue.removeFirst();
			for(Integer x:tree[current]) {
				if(tree[x].isEmpty() && arr[x]==-2)continue;
				ans[x]=arr[x]-arr[current];
				queue.addLast(x);
			}
		}
		long sum=0;
		for(int i=0;i<n;i++) {
			if(ans[i]<0) {
				out.println(-1);
				out.close();
				return;
			}else {
				sum+=ans[i];
			}
		}
		out.println(sum);
		out.close();
	}

	public static PrintWriter out;
	
	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 e) {
					e.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 e) {
				e.printStackTrace();
			}
			return str;
		}
	}
	
}
