#include <bits/stdc++.h>
using namespace std;
const long long INF = 1e18;
const long long MOD = 1e9 + 7;
const long double eps = 1e-7;
const long long zero = 0;
vector<long long> s;
vector<long long> a;
vector<vector<long long>> g;
void update(long long cur, long long gone) {
  if (s[cur] != -1 && gone > s[cur]) {
    cout << -1 << endl;
    exit(0);
  }
  if (g[cur].size() == 0) {
    a[cur] = max(a[cur], zero);
    return;
  }
  for (long long i = 0; i < g[cur].size(); ++i)
    update(g[cur][i], max(gone, s[cur]));
  if (a[cur] == -1) {
    long long m = INF;
    for (long long i = 0; i < g[cur].size(); ++i)
      m = min(m, a[g[cur][i]] - gone);
    if (m < 0) {
      cout << -1 << endl;
      exit(0);
    }
    a[cur] = m;
    for (long long i = 0; i < g[cur].size(); ++i) a[g[cur][i]] -= m + gone;
  } else {
  }
}
int32_t main() {
  ios_base::sync_with_stdio(NULL);
  cin.tie(0);
  cout.tie(0);
  cout << fixed << setprecision(10);
  long long n;
  cin >> n;
  s.assign(n, 0);
  a.assign(n, 0);
  g.assign(n, vector<long long>(0));
  for (long long i = 1; i < n; ++i) {
    long long p;
    cin >> p;
    g[p - 1].push_back(i);
  }
  for (long long i = 0; i < n; ++i) cin >> s[i];
  a[0] = s[0];
  for (long long i = 1; i < n; ++i) a[i] = s[i];
  for (long long i = 0; i < g[0].size(); ++i) update(g[0][i], a[0]);
  long long res = 0;
  for (long long i = 0; i < a.size(); ++i) {
    res += a[i];
    if (a[i] < 0) {
      cout << -1 << endl;
      return 0;
    }
  }
  cout << res << endl;
  return 0;
}
