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