#include <bits/stdc++.h>
using namespace std;
long long COMB(long long N, long long R) {
  long long L, sum = 1, i = 1;
  if (R > N / 2)
    L = N - R;
  else {
    L = R;
  }
  while (L--) {
    sum *= N--;
    sum /= i++;
  }
  return sum;
}
int main() {
  long long n, m, t, ans = 0;
  cin >> n >> m >> t;
  for (int i = 4; i <= n; i++) {
    for (int j = 1; j <= m; j++) {
      long long o = i + j;
      if (o == t) {
        ans += COMB(n, i) * COMB(m, j);
      }
    }
  }
  cout << ans;
  return 0;
}
