#include <bits/stdc++.h>
using namespace std;
const long long mod = 1e9 + 7;
int main() {
  ios_base::sync_with_stdio(0);
  long long n, m, t;
  cin >> n >> m >> t;
  long long answ = 0;
  for (long long i = 4; i < t; i++) {
    if (t - i <= m) {
      double temp = 1;
      for (long long j = 2; j <= i; j++) temp /= j;
      for (long long j = 2; j <= t - i; j++) temp /= j;
      for (long long j = 0; j < i; j++) temp *= (n - j);
      for (long long j = 0; j < t - i; j++) temp *= (m - j);
      answ += (long long)(temp + 0.1);
    }
  }
  cout << answ;
}
