#include <bits/stdc++.h>
using namespace std;
inline long long min(long long a, long long b, long long c) {
  return min(min(a, b), c);
}
inline long long max(long long a, long long b, long long c) {
  return max(max(a, b), c);
}
inline void fastio() {
  ios_base::sync_with_stdio(false), cin.tie(NULL), cout.tie(NULL);
}
int dx[] = {-1, 0, 1, 0, -1, -1, 1, 1};
int dy[] = {0, 1, 0, -1, -1, 1, 1, -1};
vector<long long> gr[2000006];
long long s[2000006];
long long dfs(long long src, long long par, long long grand_par, long long ht) {
  long long res = 0;
  if (ht % 2 == 0) {
    long long min_x = INT_MAX;
    for (auto child : gr[src]) {
      if (child != par) {
        res += dfs(child, src, par, ht + 1);
        res += s[child] - s[par];
        if (s[child] - s[par] < 0) {
          cout << "-1";
          exit(0);
        }
        min_x = min(min_x, s[child] - s[par]);
      }
    }
    if (min_x != INT_MAX) {
      res -= (min_x * (gr[src].size() - 1));
      res += min_x;
    }
  } else {
    for (auto child : gr[src]) {
      if (child != par) {
        res += dfs(child, src, par, ht + 1);
      }
    }
    if (ht == 1) res += s[1];
  }
  return res;
}
int main() {
  fastio();
  long long n;
  cin >> n;
  for (long long i = 2; i <= n; i++) {
    long long p;
    cin >> p;
    gr[p].push_back(i);
    gr[i].push_back(p);
  }
  for (long long i = 1; i <= n; i++) cin >> s[i];
  cout << dfs(1, 0, 0, 1);
  return 0;
}
