#include <iostream>

using namespace std;

/*
 * Computes the number of groups of k out of n things.
 * @pre n and k are nonnegative integers.
 * @post None.
 * @param n  The given number of things.
 * @param k  The given number to choose.
 * @return c(n, k).
 */
int kofn(int n, int k)
{
   if ( (k == 0) || (k == n) )
      return 1;
   else if (k > n)
      return 0;
   else
      return kofn(n-1, k-1) + kofn(n-1, k);
}  // end c

int main()
{
  int k, N, result;

  cout << "Computes the number of groups of k out of n things.\n";
  cout << "Enter N: ";
  cin >> N;
  cout << "Enter k: ";
  cin >> k;

  result = kofn(N, k);
  cout << "There are " << result << " number of groups of size "
       << k << " in " << N << " things\n";
  return 0;
}