#include <bits/stdc++.h>
using namespace std;
long long sum;
long long C(int n, int r) {
  long long Res = 1;
  int memo[31] = {0};
  if (r > n) return 0;
  r = max(r, n - r);
  for (int i = n; i > r; i--) {
    Res *= i;
    for (int j = n - r; j > 1; j--)
      if (!memo[j] && Res % j == 0) Res /= j, memo[j] = 1;
  }
  return Res;
}
int main() {
  int n, m, t;
  cin >> n >> m >> t;
  for (int i = 4; i <= min(n, t - 1); i++) sum += C(n, i) * C(m, t - i);
  cout << sum << endl;
}
