def findGreatestCommonDivisor(a, b):
    while a != b:
        if a > b:
            a = a - b
            return findGreatestCommonDivisor(a, b)
        elif a <= b:
            b = b - a
            return findGreatestCommonDivisor(a, b)
    return a

print findGreatestCommonDivisor(12387, 1239)