year = int(input("Which year do you want to check?"))
if year % 4 == 0:
    if year % 100 == 0:
        if year % 400 == 0:
            print("It's a leap year.")
        else:
            print("It's not a leap year.")
    else:
        print("It's a leap year.")
else:
 print("It's not a leap year.")