def is_prime(number):
    if number <= 1:
        return False
    if number <= 3:
        return True
    if number % 2 == 0 or number % 3 == 0:
        return False
    
    i = 5
    while i * i <= number:
        if number % i == 0 or number % (i + 2) == 0:
            return False
        i += 6
    
    return True

def main():
    print("Prime Number Checker")
    print("-------------------------")
    
    while True:
        try:
            num = int(input("Enter a positive integer : "))
            if num <= 0:
                print("Exiting the program.")
                break

            if is_prime(num):
                print(f"{num} is a prime number.")
            else:
                print(f"{num} is not a prime number.")
        except ValueError:
            print("Invalid input. Please enter a positive integer.")

if __name__ == "__main__":
    main()