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