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