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