#include <bits/stdc++.h>
using namespace std;
int n, m, t;
long long a[50][50], ans;
int main() {
  cin >> n >> m >> t;
  int k = max(n, m);
  for (int i = 0; i <= k; i++)
    for (int j = 0; j <= i; j++)
      if (i == 0 || j == 0 || j == i)
        a[i][j] = 1;
      else
        a[i][j] = a[i - 1][j] + a[i - 1][j - 1];
  for (int i = 4; i <= t - 1; i++) {
    if (t - i <= m && i <= n) ans += a[n][i] * a[m][t - i];
  }
  cout << ans;
  return 0;
}
