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