#include <bits/stdc++.h>
using namespace std;
int n;
vector<int> adj[100100];
long long Aval[100100], Sval[100100], sum = 0;
bool fail = false;
long long DFS(int here, int depth, long long curSum) {
  long long mn = (long long)1e15;
  for (int there : adj[here]) {
    mn = min(mn, DFS(there, depth + 1, curSum + Aval[here]));
  }
  if (depth % 2 == 1) {
    if (Sval[here] > mn) fail = true;
  } else {
    Sval[here] = mn;
  }
  return Sval[here];
}
void DFS2(int here, int depth, long long curSum) {
  if (Sval[here] == (long long)1e15) return;
  sum += Sval[here] - curSum;
  for (int there : adj[here]) {
    DFS2(there, depth + 1, Sval[here]);
  }
}
int main() {
  scanf("%d", &n);
  for (int i = 2; i <= n; i++) {
    int p;
    scanf("%d", &p);
    adj[p].push_back(i);
  }
  for (int i = 1; i <= n; i++) {
    scanf("%d", &Sval[i]);
  }
  DFS(1, 1, 0);
  DFS2(1, 1, 0);
  if (!fail)
    printf("%lld", sum);
  else
    printf("-1");
}
