# reads in 2 integers, prints their greatest common divisor
# Matt Bishop, MHI 289I, Winter 2019

#
# read in a  positive number
# caller will handle any exceptions
# we have to raise non-positive exception
#
def getnum(what):
    # read in the number (you hope)
    # if it's not a number, the ValueError exception is
    # raised automatically
    n = int(input("Please enter the %s number: " % what))
    # it's a number; now we raise an exception if it's
    # not positive
    if n <= 0:
       raise ValueError("Integer must be positive")
    # positive; return it
    return n

#
# 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)
#
# get the inputs, handle errors, and report results
#
def main():
    # read in two numbers
    try:
        m = getnum("first")
        n = getnum("second")
    # say what went wrong, if anything, and then quit
    except ValueError as errmsg:
        print("Bad number:", errmsg)
        return
    except Exception as errmsg:
        print(errmsg)
        return
    # now print the results
    print("The greatest common divisor of", m, "and", n, "is", gcd(m, n))

# now run the program
main()