#include <bits/stdc++.h>
using namespace std;
long long nCr(int n, int r) {
  if (n - r == 0) return 1;
  return nCr(n - 1, r) * (n) / (n - r);
}
int main() {
  int n, m, t;
  unsigned long long sum = 0;
  cin >> n >> m >> t;
  for (int i = 4; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      if (i + j == t) {
        sum += ((nCr(n, i)) * nCr(m, j));
      }
    }
  }
  cout << sum;
}
