#include <stdio.h>

int bsearch( int, int, int[] );

main()
{
   int f[] = {0, 1, 3, 4, 6, 7, 8, 8, 9};
   int n = 9, k = 2, res;

   res = bsearch( k, n, f );

   printf("%d\n", res );
}

int bsearch( int k, int n, int r[] )
{ int high, i, low;
  for ( low=(-1), high=n;  high-low > 1;  )
      {
        i = (high+low) / 2;
            if ( k <= r[i] )  high = i;
            else             low  = i;
       }
     if ( k==r[high] )  return( high );
          else              return( -1 );
}