#include<stdio.h>
int checkIfPrime(int x);
long factorial(int x);
int main()
{
  //int low=0,high=0;
  int number = 0;
  printf("Enter the number: (< 20) as factorial goes out of bounds:");
  scanf("%d",&number);
  if(number < 1)
  {
    printf("Wrong Input: Positive integer required \n");
  }
  else if (number == 1)
  {
    printf("You have entered 1. Not a prime \n");
  }
  else
  {
    if(checkIfPrime(number) == 1)
      printf("%d is a prime number \n",number);
    else
      printf("%d is NOT a prime number \n",number);
  }
  
  return 0;
}
int checkIfPrime(int x)
{
  if( ( factorial(x-1) + 1) % x == 0)
    return 1;
  else
    return 0;
  
}
long factorial(int x)
{
  long fact = 1;
  int i =1;
  for( i = 1; i<= x ; i++)
  {
    fact = fact * i;
  }
  return fact;
}