// A optimized school method based C++ program to check 
// if a number is composite. 
#include <stdio.h> 
   
int isComposite(int n) 
{ 
    // Corner cases 
    if (n <= 1)  return false; 
    if (n <= 3)  return false; 
   
    // This is checked so that we can skip  
    // middle five numbers in below loop 
    if (n%2 == 0 || n%3 == 0) return true; 
   
    for (int i=5; i*i<=n; i=i+6) 
        if (n%i == 0 || n%(i+2) == 0) 
           return true; 
   
    return false; 
} 
   
   
// Driver Program to test above function 
int main() 
{ 
int n;
printf("nhap n: "); scanf("%d",&n);
    if(isComposite(n) ==true){
    	printf("%d la hop so.",n);
	}
	else
	printf("%d khong phai la hop so.",n);

    return 0; 
}