#include <bits/stdc++.h>
using namespace std;
const long long M = 998244353;
const long long oo = 1e18;
struct tree {
  long long sum = 0, mx = 0, ro = 0;
  vector<int> n;
} s[100010];
long long n, p[100010], s1[100010], s2[100010];
void check(int v, int sm) {
  if (s1[v] == -1) {
    s1[v] = sm;
  } else {
    if (sm > s1[v]) {
      cout << -1 << endl;
      exit(0);
    }
    s2[v] = s1[v] - sm;
  }
  for (auto x : s[v].n) {
    check(x, s1[v]);
  }
}
int main() {
  cin >> n;
  for (int i = 2; i <= n; ++i) {
    cin >> p[i];
    s[p[i]].n.push_back(i);
  }
  for (int i = 1; i <= n; ++i) {
    cin >> s1[i];
    s[i].sum = s1[i];
    s[i].ro = s1[i];
  }
  check(1, 0);
  for (int i = n; i > 0; --i) {
    if (s[i].ro == -1) {
      if (!s[i].n.size()) continue;
      long long mn = oo;
      for (auto x : s[i].n) {
        mn = min(mn, s2[x]);
      }
      s2[i] += mn;
      for (auto x : s[i].n) {
        s2[x] -= mn;
      }
    }
  }
  long long ans = 0;
  for (int i = 1; i <= n; ++i) {
    ans += s2[i];
  }
  cout << ans << endl;
}
