public class Binom {
  public static void main(String[] args) {
    System.out.println(binomial(4,2));
  }
  
  public static long binomial(int n, int k) {
  	if (k == 0) { return(1); } else
		return( binomial(n, k-1) * (n-k+1)/k );
  }	
}