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 Main {
	static BufferedReader br;
	static PrintWriter pr;
	static int cin() throws Exception
	{
		return Integer.valueOf(br.readLine());
	}
	static int[] split() throws Exception
	{
		String[] cmd=br.readLine().split(" ");
		int[] ans=new int[cmd.length];
		for(int i=0;i<cmd.length;i++)
		{
			ans[i]=Integer.valueOf(cmd[i]);
		}
		return ans;
	}
	static long[] splitL() throws IOException
	{
		String[] cmd=br.readLine().split(" ");
		long[] ans=new long[cmd.length];
		for(int i=0;i<cmd.length;i++)
		{
			ans[i]=Long.valueOf(cmd[i]);
		}
		return ans;
	}
	static int sum(long n)
	{
		int ans=0;
		while(n!=0)
		{
			ans=ans+(int)(n%10);
			n=n/10;
		}
		return ans;
	}
	static long gcd(long x,long y)
	{
		if(x==0)
			return y;
		if(y==0)
			return x;
		if(x>y)
			return gcd(x%y,y);
		else
			return gcd(x,y%x);
	}
	static ArrayList<Integer>[]gr;
	static int[]p;
	static int[]sv;
	static int[]vis;
	static int[]val;
	static Exception e;
	static void dfs(int node,int par) throws Exception
	{
		if(sv[node]!=-1)
		{
			val[node]=sv[node]-sv[par];
		}
		else
		{
			if(gr[node].size()==1)
			{
				val[node]=0;
				sv[node]=sv[par];
			}
			else
			{
				int min=1000000000;
				for(int i=0;i<gr[node].size();i++)
				{
					int y=gr[node].get(i);
					if(vis[y]==0)
					min=Math.min(min, sv[y]);
				}
				if(sv[par]>min)
				{
					throw e;
				}
				else
				{
					val[node]=min-sv[par];
					sv[node]=min;
//					System.out.println(node+" "+sv[node]+" "+" "+par+" "+sv[par]+" "+min);
				}
			}
		}
		for(int i=0;i<gr[node].size();i++)
		{
			int y=gr[node].get(i);
			if(vis[y]==1)
				continue;
			vis[y]=1;
			dfs(y,node);
		}
	}
	public static void main(String[] args) throws Exception{
		// TODO Auto-generated method stub
		br=new BufferedReader(new InputStreamReader(System.in));
		pr=new PrintWriter(new OutputStreamWriter(System.out));
		int cases=1;
		while(cases!=0)
		{
			cases--;
			int n=cin();
		    p=split();
			gr=new ArrayList[n+1];
			for(int i=0;i<=n;i++)
			{
				gr[i]=new ArrayList<>();
			}
			for(int i=2;i<=n;i++)
			{
				int x=i;
				int y=p[i-2];
				gr[x].add(y);
				gr[y].add(x);
			}
			int[]f=split();
			sv=new int[n+1];
			for(int i=1;i<=n;i++)
			{
				sv[i]=f[i-1];
			}
			long ans=0;
			vis=new int[n+1];
			val=new int[n+1];
			vis[1]=1;
			try {
			dfs(1,0);
//			System.out.println(Arrays.toString(val));
			for(int i=1;i<=n;i++)
			{
				ans=ans+(long)val[i];
			}
			System.out.println(ans);
			}
			catch(Exception e)
			{
				System.out.println(-1);
			}
		}
	}
}
