https://codeforces.com/contest/1099/problem/D

题解：对于每个-1，如果有子节点则最大化，无子节点则最小化。

/*
*@Author:   STZG
*@Language: C++
*/
#include <bits/stdc++.h>
#include<iostream>
#include<algorithm>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<bitset>
#include<queue>
#include<deque>
#include<stack>
#include<cmath>
#include<list>
#include<map>
#include<set>
//#define DEBUG
#define RI register int
using namespace std;
typedef long long ll;
//typedef __int128 lll;
const int N=200000+10;
const int MOD=1e9+7;
const double PI = acos(-1.0);
const double EXP = 1E-8;
const int INF = 0x3f3f3f3f;
int t,n,m,k,q;
ll ans;
ll a[N];
vector<int>G[N];
char str;
void  dfs(int rt,int m){
    if(a[rt]==-1){
		ll tmp = INF;
		for(int v:G[rt])tmp = min(tmp,a[v]);	if(tmp==INF) tmp=m;
		a[rt]=tmp;
	}
	if(a[rt]-m<0){
        cout<<-1<<endl;//printf("%d",rt);
        exit(0);
    }

    ans += a[rt]-m;
    for(int v:G[rt])
        dfs(v,a[rt]);
}
int main()
{
#ifdef DEBUG
	freopen("input.in", "r", stdin);
	//freopen("output.out", "w", stdout);
#endif
    scanf("%d",&n);
    for(int i=2;i<=n;i++){
        scanf("%d",&t);
        G[t].push_back(i);
        //for(int v:G[t])cout<<v<<t;
    }
    for(int i=1;i<=n;i++){
        scanf("%I64d",&a[i]);
    }
    ans=0;
    dfs(1,0);
    cout<<ans<<endl;
    //cout << "Hello world!" << endl;
    return 0;
}