/* Utilities */
# include <limits.h>

# include <stdio.h>

int choose(int n, int r);

int choose(int n, int r)
{
  int i,ans;
  if (r<0 && n<0) {printf("Error in choose, %d, %d", n, r); exit(0);}
  if (r == 0) return 1;
  if (r < 0)  return 0;
  if (n < r)  return 0;
  if (n == r) return 1;
  if (r > n-r) r = n-r;
  ans = 1;
  for (i=0; i < r; i++) 
  {
    if ( (INT_MAX)/(n-i) >= ans )  {ans *= n-i; ans /= i+1;}
    else
    {
      printf("Overflow in choose.\n"); exit(0);
    }
  }
  return ans;
}