# reads in 2 integers, prints their greatest common divisor
# ECS 10, May 29, 2009
# Matt Bishop

# read in a number
# parameters: none
# returns: 2 values
#     1st: the number, if read successfully
#          0, on EOF
#          -1, if not EOF and not successful
#     2nd: True, if list read successfully; False, if not
def getnum():
    # read the input
    # catch any problems and bail out at once
    try:
        # read in ... something (a number, supposedly)
        n = input("Enter an integer: ")
        # this causes a TypeError if not a number
        n += 0
    except EOFError:
        # didn't enter anything
        return 0, False
    except (NameError, TypeError, SyntaxError):
        # entered something bogus
        print "Please enter an integer"
        return -1, False
    # return the value read
    return n, True

# recursively compute the GCD of two numbers
# parameters: m, n are the numbers
# returns: the number of positive integers in the list
def gcd(m, n):
    # base case: if n is 0, the other is the GCD
    if n == 0:
        return m
    # recursion here
    # this just is the Euclidean algorithm
    else:
        return gcd(n, m % n)

# this puts it all together
def main():
    # get the first number
    m, okay = getnum()
    # if it's not an integer, give an error
    if okay and m != int(m):
        print m, "is not an integer"
    # all's well -- get the next number
    elif okay:
        n, okay = getnum()
        # if it's not an integer, give an error
        if okay and n != int(n):
            print n, "is not an integer"
        # got both numbers -- print the GCD
        elif okay:
            print "The greatest common divisor of", m, "and", n, "is", gcd(m,n)

main()