#include <bits/stdc++.h>
using namespace std;
long long MAX = 1000000000;
long long MOD = 1000000007;
long long ncr(long long n, long long m) {
  long long a = 1, k = 1;
  for (long long i = n; i > n - m; i--) {
    a *= i;
    if (k <= m) a /= k;
    k++;
  }
  return a;
}
int main() {
  ios_base::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  long long test = 1;
  while (test--) {
    long long n;
    cin >> n;
    long long m;
    cin >> m;
    long long t;
    cin >> t;
    ;
    long long ans = 0;
    for (long long i = (4); i < (t); i++) {
      if (i <= n && t - i <= m) {
        ans += ncr(n, i) * ncr(m, t - i);
      }
    }
    cout << ans;
  }
}
