#include <bits/stdc++.h>
using namespace std;
const int N = 110000;
vector<int> adj[N];
long long p[N], s[N];
int main() {
  ios::sync_with_stdio(0);
  int n;
  cin >> n;
  for (int i = 2; i <= n; i++) cin >> p[i];
  for (int i = 1; i <= n; i++) cin >> s[i];
  for (int i = 1; i <= n; i++) {
    if (~s[i]) {
      int j = p[p[i]];
      int k = p[i];
      if (s[i] < s[j]) return puts("-1"), 0;
      adj[k].push_back(s[i] - s[j]);
    }
  }
  long long dap = s[1];
  for (int i = 1; i <= n; i++) {
    if (!adj[i].empty()) {
      sort(adj[i].begin(), adj[i].end());
      dap += adj[i][0];
      for (int x : adj[i]) dap += (x - adj[i][0]);
    }
  }
  cout << dap << endl;
  return 0;
}
