#include <stdio.h>
#define MaxPrimes 50
int Prime[MaxPrimes], UpperBound;

void CheckPrime ( int K) {
  int J ;

// the plan : see i f J divides K, f o r a l l values J which are
// (a) themselves prime (no need to t r y J i f i t i s nonprime ) , and
// (b) less than or equal to s q r t (K) ( i f K has a d i v i s o r l a r g e r
// than t h i s square root , i t must also have a smaller one ,
// so no need to check f o r l a r g e r ones)

  J = 2;
//   while ( 1 ) {
  for(J=2; J*J <= K; J++){
  if ( Prime [ J ] == 1)
    if (K % J == 0) {
      Prime [K] = 0;
      return ;
    }
    J++;
  }
  Prime[K]=1;

}

main()
   {  int N;
      printf("enter upper bound\n");
      scanf("%d", &UpperBound);
      Prime[2] = 1;
      for (N = 3; N <= UpperBound; N += 2){
         CheckPrime(N);
         if (Prime[N]) printf("%d is a prime\n",N);
      }
      return 0;
   }