#include <bits/stdc++.h>
using namespace std;
long long c[32][32];
int main() {
  int n, m, t;
  cin >> n >> m >> t;
  long long fact[32], inv[32];
  fact[0];
  for (int i = 1; i <= 31; i++) {
    for (int j = 0; j < i + 1; j++) {
      if (j == i || j == 0) {
        c[i][j] = 1;
        continue;
      }
      c[i][j] = c[i - 1][j - 1] + c[i - 1][j];
    }
  }
  int i = 4;
  long long ans = 0;
  while (i <= n) {
    if (t - i > 0 && m >= t - i) {
      ans += c[n][i] * c[m][t - i];
    }
    i++;
  }
  cout << ans;
}
