>>7
#include<stdio.h>
int main(void)
{
  int n,i,flg=0;;
  printf("n: ");scanf("%d",&n);
  if(n<2)return -1;
  for(i=2;i<=n/2;i++)if(!(n%i)){flg=1;break;}
  printf("%d is%sprime number.\n",n,flg?" not ":" ");
  return 0;
}