#include <bits/stdc++.h>
using namespace std;
long long combinaciones(int n, int r) {
  if (r > n) return 0;
  int q = abs(n - r), menor = min(q, r);
  double res = 1;
  for (int i = n; i > max(q, r); i--) {
    res = (double)(res * (double)(i));
    if (menor > 1) {
      res = (double)(res / (double)(menor));
      menor--;
    }
  }
  return ((long long)(res + 1E-9));
}
int main() {
  int n, m, t;
  while (cin >> n >> m >> t) {
    if (n > 3 && m > 0 && n + m >= t) {
      long long total = 0;
      for (int i = 4; i <= n; i++) {
        if (t - i >= 1) {
          long long boys = (long long)combinaciones(n, i);
          long long girl = (long long)combinaciones(m, t - i);
          total = (long long)(total + (long long)(boys * girl));
        }
      }
      cout << total << endl;
    } else
      cout << 0 << endl;
  }
  return 0;
}
