#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const double pi = acos(-1.0);
int n, m, t;
long long c[50][50];
int main() {
  cin >> n >> m >> t;
  c[0][0] = 1;
  for (int i = 1; i <= 30; ++i) {
    c[i][0] = 1;
    for (int j = 1; j <= 30; ++j) c[i][j] = c[i - 1][j - 1] + c[i - 1][j];
  }
  long long ans = 0;
  for (int boys = 4; t - boys >= 1 && boys <= n; ++boys) {
    if (t - boys <= m) ans += c[n][boys] * c[m][t - boys];
  }
  cout << ans;
  return 0;
}
