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

public class A {
	static ArrayList<Integer> [] adj;
	static long sum;
	static int [] s;
	static void dfs(int u, int p, int sp){
		int my = s[u] - sp;
		if(s[u] == -1){
			my = adj[u].isEmpty()?0:Integer.MAX_VALUE;
			for(int v:adj[u]){
				if(v != p)
					my = Math.min(my, s[v] - sp);
			}
		}
		sum = sum == -1 || my < 0?-1:sum+my;
		for(int v:adj[u]){
			if(v != p)
				dfs(v, u, sp+my);
		}
	}
	public static void main(String[] args) throws NumberFormatException, IOException {
		Scanner sc = new Scanner();
		PrintWriter out = new PrintWriter(System.out);
		int n = sc.nextInt();
		adj = new ArrayList[n];
		for (int i = 0; i < adj.length; ++i) {
			adj[i] = new ArrayList<>();
		}
		for (int i = 1; i < n; ++i) {
			adj[sc.nextInt()-1].add(i);
		}
		s = new int[n];
		for (int i = 0; i < s.length; ++i) {
			s[i] = sc.nextInt();
		}
		sum = 0;
		dfs(0, -1, 0);
		out.println(sum);
		out.close();

	}


	static class Scanner {
		BufferedReader br;
		StringTokenizer st;

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

		public String next() throws IOException {
			while (st == null || !st.hasMoreTokens()) {
				st = new StringTokenizer(br.readLine());
			}
			return st.nextToken();
		}

		public int nextInt() throws NumberFormatException, IOException {
			return Integer.parseInt(next());
		}
		public long nextLong() throws NumberFormatException, IOException {
			return Long.parseLong(next());
		}
	}

}
