def main():
    number = int(input("Enter a credit card number as a long integer: "))
    
    if isValid(number):
        print(number, "is valid")
    else:
        print(number, "is invalid")

# Return true if the card number is valid 
def isValid(number):
    return getSize(number) >= 13 and getSize(number) <= 16 and \
        (prefixMatched(number, 4) or prefixMatched(number, 5) or \
        prefixMatched(number, 6) or prefixMatched(number, 37)) and  \
       (sumOfDoubleEvenPlace(number) + sumOfOddPlace(number)) % 10 == 0

# Get the result from Step 2 
def sumOfDoubleEvenPlace(number): 
    result = 0
    
    number = number // 10 # Starting from the second digit from left
    while number != 0:
        result += getDigit((number % 10) * 2)
        number = number // 100 # Move to the next even place
    
    return result
  
# Return this number if it is a single digit, otherwise, return 
# the sum of the two digits 
def getDigit(number):
    return number % 10 + (number // 10)
  
# Return sum of odd place digits in number 
def sumOfOddPlace(number): 
    result = 0
   
    while number != 0:
        result += number % 10
        number = number // 100 # Move two positions to the left

    return result
  
# Return true if the digit d is a prefix for number
def prefixMatched(number, d):
    return getPrefix(number, getSize(d)) == d
  
# Return the number of digits in d 
def getSize(d): 
    numberOfDigits = 0
    
    while d != 0:
        numberOfDigits += 1
        d = d // 10
    
    return numberOfDigits
  
# Return the first k number of digits from number. If the 
# number of digits in number is less than k, return number. 
def getPrefix(number, k):
    result = number
    
    for i in range(getSize(number) - k):
        result //= 10
    
    return result

main()