# Determine if a number entered by the user is
# prime or not.
# Improvements to original program.
# 1. We only need to go up to the square root
#    of the number.
# 2. The only even number we check is 2.
import math


def main():
    """Determine if a number entered by the user is prime or not."""
    number = int(input("Please enter a number greater than"
                       + " or equal to 2: "))

    # Special case for 2, the only even prime.
    prime = number == 2 or number % 2 != 0
    # If number is not even then we only need to divide
    # by odd numbers.
    divisor = 3

    limit = math.sqrt(number)
    while divisor <= limit and prime:
        prime = number % divisor != 0
        divisor += 1
    if prime:
        print(number, "is prime.")
    else:
        print(number, "is not prime.")
    # OR print(number, " is",
    #      "not" if not prime else "", " prime", sep="")


main()