#include <bits/stdc++.h>
using namespace std;
const int N = 100000, INF = 0x3f3f3f3f;
int eo[N], *ej[N], ss[N];
void append(int i, int j) {
  int o = eo[i]++;
  if (o >= 2 && (o & o - 1) == 0)
    ej[i] = (int *)realloc(ej[i], (o << 1) * sizeof *ej[i]);
  ej[i][o] = j;
}
long long dfs(int p, int i, int h) {
  long long ans = 0;
  if (h % 2 == 0) {
    if (eo[i] == 1) return 0;
    int s = INF;
    for (int o = eo[i]; o--;) {
      int j = ej[i][o];
      if (j != p)
        if (ss[j] >= ss[p])
          s = min(s, ss[j] - ss[p]);
        else
          return -1;
    }
    ans += s;
    for (int o = eo[i]; o--;) {
      int j = ej[i][o];
      if (j != p) ans += ss[j] - ss[p] - s;
    }
    for (int o = eo[i]; o--;) {
      int j = ej[i][o];
      if (j != p) {
        long long ans_ = dfs(i, j, h + 1);
        if (ans_ != -1)
          ans += ans_;
        else
          return -1;
      }
    }
  } else {
    for (int o = eo[i]; o--;) {
      int j = ej[i][o];
      if (j != p) {
        long long ans_ = dfs(i, j, h + 1);
        if (ans_ != -1)
          ans += ans_;
        else
          return -1;
      }
    }
  }
  return ans;
}
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) ej[i] = (int *)malloc(2 * sizeof *ej[i]);
  for (int j = 1; j < n; j++) {
    int i;
    cin >> i, i--;
    append(i, j), append(j, i);
  }
  for (int i = 0; i < n; i++) cin >> ss[i];
  long long ans = dfs(-1, 0, 1);
  if (ans == -1) {
    cout << "-1\n";
    return 0;
  }
  ans += ss[0];
  cout << ans << '\n';
  for (int i = 0; i < n; i++) free(ej[i]);
  return 0;
}
