prime numbers program

#include<stdio.h>
#include<conio.h>
void main()
{
int a;
clrscr();
printf("Enter a number which you want to check it is prime or not=");
scanf("%d",&a);
 if(a%2==0 || a%3==0 || a%5==0)
{
printf("%d number is not prime");
}
else
{
printf("its a prime number");
}
getch();
}