#include <bits/stdc++.h>
using namespace std;
long long mod = 1e9 + 7;
int dp[31][31];
long long bin(long long n, long long t) {
  if (dp[n][t] != 0) return dp[n][t];
  if (t == 0 || t == n)
    dp[n][t] = 1;
  else
    dp[n][t] = bin(n - 1, t - 1) + bin(n - 1, t);
  return dp[n][t];
}
int main() {
  long long n, m, t;
  cin >> n >> m >> t;
  long long ans = 0;
  for (int x = 4; x <= n; ++x) {
    for (int y = 1; y <= m; ++y) {
      if (x + y == t) {
        ans += (bin(n, x) * bin(m, y));
      }
    }
  }
  cout << ans;
}
