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.util.*;
import java.io.*;

public class D{
	
    static class FastReader 
    { 
        BufferedReader br; 
        StringTokenizer st; 
  
        public FastReader() 
        { 
            br = new BufferedReader(new
                     InputStreamReader(System.in)); 
        } 
  
        String next() 
        { 
            while (st == null || !st.hasMoreElements()) 
            { 
                try
                { 
                    st = new StringTokenizer(br.readLine()); 
                } 
                catch (IOException  e) 
                { 
                    e.printStackTrace(); 
                } 
            } 
            return st.nextToken(); 
        } 
  
        int nextInt() 
        { 
            return Integer.parseInt(next()); 
        } 
  
        long nextLong() 
        { 
            return Long.parseLong(next()); 
        } 
  
        double nextDouble() 
        { 
            return Double.parseDouble(next()); 
        } 
  
        String nextLine() 
        { 
            String str = ""; 
            try
            { 
                str = br.readLine(); 
            } 
            catch (IOException e) 
            { 
                e.printStackTrace(); 
            } 
            return str; 
        } 
    }
    public static boolean bfsAgain(LinkedList<Integer> ar[],int value[],int sum[],int c)
    {
    	Queue<Integer> q = new LinkedList<>();
    	q.add(c);
    	int x = 0,y = 0;
    	while(!q.isEmpty())
    	{
    		x = q.poll();
    		Iterator<Integer> itr = ar[x].iterator();
    		while(itr.hasNext())
    		{	
    			y = itr.next();
    			q.add(y);
    			if(sum[y] != -1)
    			{	
    				if(sum[x] > sum[y])
    				{
    					return false;
    				}
    				value[y] = sum[y]-sum[x];
    				
    			}
    			else value[y] = 0;
    		}
    	}
    	return true;
    }
    public static void bfsUtil(LinkedList<Integer> ar[],int sum[],int c)
    {
    	Queue<Integer> q = new LinkedList<>();
    	q.add(c);
    	int x = 0;
    	int y = 0;
    	while(!q.isEmpty())
    	{
    		x = q.poll();
    		Iterator<Integer> itr = ar[x].iterator();
    		if(sum[x] != -1)
    		{
    		while(itr.hasNext())
    		{
    			y = itr.next();
    			q.add(y);
    		}
    		}
    		else
    		{
    			int mins = Integer.MAX_VALUE;
    			while(itr.hasNext())
    			{
    				y = itr.next();
    				if(sum[y] < mins) mins = sum[y];
    				q.add(y);
    			}
    			if(mins == Integer.MAX_VALUE)
    			sum[x] = -1;
    			else sum[x] = mins;
    		}
    		//System.out.println(x+" "+sum[x]);
    	}
    }
	public static void main(String[] args) 
	{
		FastReader sc = new FastReader();
		int n = sc.nextInt();
		LinkedList<Integer> ar[] = new LinkedList[n+1];
		int value[] = new int[n+1];
		int sum[] = new int[n+1];
		for(int i = 0; i <= n; i++)
		{
			ar[i] = new LinkedList<>();
		}
		int x = 0;
		for(int i = 2; i <= n; i++)
		{
			x = sc.nextInt();
			ar[x].add(i);
		}
		for(int i = 1; i <= n; i++)
		{
			sum[i] = sc.nextInt();
		}
		value[1] = sum[1];
		bfsUtil(ar,sum,1);
		if(!bfsAgain(ar,value,sum,1))
		{
			System.out.println(-1);
			return;
		}
		//System.out.println(Arrays.toString(sum));
		//System.out.println(Arrays.toString(value));
		long sumv = 0;
		for(int i = 1; i <= n; i++)
		{
			sumv += (long)value[i];
		}
		System.out.println(sumv);
	}

}

