#include <bits/stdc++.h>
using namespace std;
unsigned long long mod = 1e9 + 7;
unsigned long long ncr(long long int n, long long int k) {
  unsigned long long res = 1;
  if (k > n - k) k = n - k;
  for (int i = 0; i < k; ++i) {
    res *= (n - i);
    res /= (i + 1);
    res = res;
  }
  return res;
}
bool prime(unsigned long long num) {
  bool flag = true;
  for (unsigned long long i = 2; i * i <= num; i++) {
    if (num % i == 0) {
      flag = false;
      break;
    }
  }
  return flag;
}
long long ipow(long long base, long long exp) {
  long long result = 1;
  for (;;) {
    if (exp & 1) {
      result *= base;
      result = result % mod;
    }
    exp >>= 1;
    if (!exp) break;
    base *= base;
    base = base % mod;
  }
  return result % mod;
}
long long abs(long long a, long long b) {
  if ((a - b) > 0)
    return (a - b);
  else
    return (b - a);
}
long long MOD = 998244353;
long long add(long long a, long long b) {
  a += b;
  if (a >= mod) a -= mod;
  if (a < 0) a += mod;
  return a;
}
long long gcd(long long a, long long b) {
  if (b == 0) return a;
  return gcd(b, a % b);
}
long long der(int k) {
  long long res = 0;
  long long fact = 1;
  for (int i = 2; i <= k; i++) fact *= i;
  int s = 1;
  long long j = 1;
  for (int i = 2; i <= k; i++) {
    j = j * i;
    long long first = (fact / j) * s;
    res += first;
    s = s * -1;
  }
  return res;
}
vector<int> v[200005];
bool visit[200005];
long long sv[200005];
long long ans = 0;
long long av[200002 + 1];
void dfs(int node, int par) {
  visit[node] = true;
  if (sv[node] == -1) {
    long long mn = INT_MAX;
    long long a = av[par];
    for (int i = 0; i < v[node].size(); i++) {
      if (!visit[v[node][i]]) mn = min(mn, sv[v[node][i]] - sv[par]);
    }
    if (mn == INT_MAX) mn = 0;
    av[node] = mn;
    sv[node] = sv[par] + av[node];
    if (mn < 0) {
      cout << "-1";
      exit(0);
    }
  } else {
    av[node] = sv[node] - sv[par];
  }
  for (int i = 0; i < v[node].size(); i++)
    if (!visit[v[node][i]]) dfs(v[node][i], node);
  ans += av[node];
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int a;
    cin >> a;
    v[a].push_back(i + 1);
    v[i + 1].push_back(a);
  }
  for (long long i = 0; i < n; i++) {
    cin >> sv[i + 1];
  }
  long long av[n + 1];
  av[1] = sv[1];
  visit[1] = true;
  ans = av[1];
  for (int i = 0; i < v[1].size(); i++) dfs(v[1][i], 1);
  cout << ans;
}
