#include <bits/stdc++.h>
using namespace std;
long long int dp[31][16];
long long int comb(long long int n, long long int r) {
  if (n - r < r) r = n - r;
  if (r == 0)
    return 1LL;
  else if (r == 1)
    return n;
  else if (n == r)
    return 1;
  else if (dp[n][r] != -1)
    return dp[n][r];
  else {
    dp[n][r] = comb(n - 1, r - 1) + comb(n - 1, r);
    return dp[n][r];
  }
}
int main() {
  for (long int i = 0; i <= 30; i++) {
    for (long int j = 0; j < 16; j++) dp[i][j] = -1;
  }
  long long int n, m, t;
  cin >> n >> m >> t;
  long long int ans = 0;
  for (long long int b = 4, g = t - 4; b <= n && g >= 1; b++, g--) {
    if (m >= g) {
      ans += comb(n, b) * comb(m, g);
    }
  }
  cout << ans << endl;
  return 0;
}
