#include <bits/stdc++.h>
using namespace std;
long long dp[40][40];
long long nCr(long long n, long long r) {
  if (n < r) return 0;
  if (n == 1 || n == 0) return dp[n][r] = 1;
  if (r == 1) return dp[n][r] = n;
  if (n == r) return 1;
  if (dp[n][r] != 0) return dp[n][r];
  return dp[n][r] = nCr(n - 1, r - 1) + nCr(n - 1, r);
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long i, j, n, m, t;
  cin >> n >> m >> t;
  long long ans = 0;
  for (i = 4; i <= n; i++) {
    if (t - i == 0) break;
    ans += nCr(n, i) * nCr(m, t - i);
  }
  cout << ans << endl;
}
