#include <bits/stdc++.h>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
using pii = pair<int, int>;
using pll = pair<LL, LL>;
LL C[31][31];
void precalc_comb() {
  C[1][1] = 1;
  for (int n = 0; n <= 30; ++n) {
    C[n][0] = C[n][n] = 1;
  }
  for (int n = 1; n <= 30; ++n) {
    for (int k = 1; k <= n / 2; ++k) {
      C[n][k] = C[n][n - k] = C[n - 1][k - 1] + C[n - 1][k];
    }
  }
}
int main() {
  precalc_comb();
  cin.sync_with_stdio(0);
  int n, m, t;
  cin >> n >> m >> t;
  LL res = 0;
  for (int nr_boys = max(4, t - m); nr_boys <= min(n, t - 1); ++nr_boys) {
    res += C[n][nr_boys] * C[m][t - nr_boys];
  }
  cout << res;
}
