def doLuhn(s, evenPos):
    s = str(s)
    sum = 0
    for d in reversed(s):
	d = int(d)
        assert 0 <= d <= 9
        if evenPos:
            d *= 2
            if d > 9:
                d = (d % 10) + 1
        sum += d
        evenPos = not evenPos
    return sum

def luhnValidation(n):
    return doLuhn(n, False) % 10 == 0

def generateCheckDigit(n):
    return 10 - (doLuhn(n, True) % 10)

if __name__ == '__main__':
    import sys
    
    if len(sys.argv) < 2:
        print "%s <number> [g]" % sys.argv[0]
	sys.exit(1)
    elif len(sys.argv) == 2:
	n = sys.argv[1]
	if luhnValidation(n):
	    print "%s is valid" % n
	else:
	    print "%s is not valid" % n
    else:
	n = sys.argv[1]
	print "%s%s" % (n, generateCheckDigit(n))