#include <bits/stdc++.h>   using namespace std;   long long int XpowerY(long long int x, long long int y, long long int m) {     long long int ans = 1;     x = x % m;     while (y > 0) {       if (y % 2 == 1) ans = (ans * x) % m;       x = ((x % m) * (x % m)) % m;       y = y >> 1;     }     return ans % m;   }   vector<long long int> gr[100023];   long long int s[100023], val[100023];   long long int fl, minP;   long long int dfs(long long int node, long long int prev, long long int lev) {     long long int mx = 1e12;     if (lev % 2 == 0) {       for (int i = 0; i < gr[node].size(); i++) {         if (s[gr[node][i]] < prev) fl = 1;         mx = min(mx, s[gr[node][i]] - prev);       };       val[node] = mx;       if (gr[node].size() == 0) val[node] = 0;     }     for (int i = 0; i < gr[node].size(); i++) {       val[gr[node][i]] = s[gr[node][i]] - mx - prev;       long long int temp;       if (lev % 2 == 0)         temp = prev + val[node];       else         temp = s[node];       dfs(gr[node][i], temp, lev + 1);     }     return 0;   }   int main() {     long long int n, x;     cin >> n;     for (long long int i = 0; i < n - 1; i++) {       cin >> x;       gr[x].push_back(i + 2);     }     for (long long int i = 1; i <= n; i++) cin >> s[i];     dfs(1, -1, 1);     val[1] = s[1];     if (fl) return cout << -1 << endl, 0;     for (long long int i = 0; i < n; i++) {       ;       minP += val[i + 1];     }     cout << minP << endl;     return 0;   }   