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 CF1098A {
	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int n = Integer.parseInt(br.readLine());
		StringTokenizer st = new StringTokenizer(br.readLine());
		int[] pp = new int[n];
		for (int i = 1; i < n; i++)
			pp[i] = Integer.parseInt(st.nextToken()) - 1;
		st = new StringTokenizer(br.readLine());
		int[] upper = new int[n];
		int[] lower = new int[n];
		for (int i = 0; i < n; i++)
			lower[i] = upper[i] = Integer.parseInt(st.nextToken());
		for (int i = 1; i < n; i++) {
			int p = pp[i];
			if (lower[p] != -1 && (lower[i] == -1 || lower[i] < lower[p]))
				lower[i] = lower[p];
		}
		for (int i = n - 1; i > 0; i--) {
			int p = pp[i];
			if (upper[i] != -1 && (upper[p] == -1 || upper[p] > upper[i]))
				upper[p] = upper[i];
		}
		for (int i = 0; i < n; i++)
			if (lower[i] != -1 && upper[i] != -1 && lower[i] > upper[i]) {
				System.out.println(-1);
				return;
			}
		long sum = upper[0];
		for (int i = 1; i < n; i++) {
			int p = pp[i];
			if (upper[i] != -1)
				sum += upper[i] - upper[p];
		}
		System.out.println(sum);
	}
}
