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