#include <bits/stdc++.h>
using namespace std;
long long c[32][32];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long n, m, t, sum = 0;
  cin >> n >> m >> t;
  for (long long i = 1; i <= 32; i++) {
    for (long long j = 0; j <= i; j++) {
      if (j == 0 || j == i) {
        c[i][j] = 1;
      } else {
        c[i][j] = c[i - 1][j - 1] + c[i - 1][j];
      }
    }
  }
  for (long long k = 4; k <= n; k++) {
    if (t - k >= 1 && t - k <= m) {
      sum += (c[n][k] * c[m][t - k]);
    }
  }
  cout << sum;
  return 0;
}
