#include <bits/stdc++.h>
using namespace std;
long long comb(long long n, long long k) {
  long long coeff = 1;
  for (long long i = 0; i < k; i++) {
    coeff *= n - i;
    coeff /= (i + 1);
  }
  return coeff;
}
int main() {
  long long n, m, t;
  cin >> n >> m >> t;
  long long answer = 0;
  for (long long i = 4; i <= t - 1 && i <= n; i++) {
    answer += comb(n, i) * comb(m, t - i);
  }
  cout << answer;
  return 0;
}
