#include <bits/stdc++.h>
using namespace std;
const int PI = acos(-1);
const int MAXN = 1e6;
unsigned long long comb(unsigned long long n, unsigned long long k) {
  if (k > n) return 0;
  unsigned long long u = 1;
  for (unsigned long long i = 1; i <= k; i++) {
    u *= n--;
    u /= i;
  }
  return u;
}
int main() {
  unsigned long long n, m, t;
  while (cin >> n >> m >> t) {
    unsigned long long ans = 0;
    for (unsigned long long boys = 4; boys <= n; boys++) {
      unsigned long long girls = t - boys;
      if (girls > m) continue;
      if (t < 1 + boys) break;
      ans += comb(n, boys) * comb(m, girls);
    }
    cout << ans << endl;
  }
  return 0;
}
