#include <bits/stdc++.h>
using namespace std;
long long nCr[31][31];
void pre() {
  for (int i = 1; i <= 30; i++) {
    nCr[i][0] = 1;
    nCr[i][1] = i;
  }
  for (int i = 2; i <= 30; i++) {
    for (int j = 1; j <= 30; j++) {
      nCr[i][j] = nCr[i - 1][j - 1] + nCr[i - 1][j];
    }
  }
}
int main() {
  int n, m, t;
  pre();
  cin >> n >> m >> t;
  unsigned long long ans = 0;
  for (int i = 4; i <= t - 1 and i <= n; i++) {
    if (t - i <= m) ans += (1LL * nCr[n][i] * nCr[m][t - i]);
  }
  cout << ans << endl;
  return 0;
}
