MuckChecker

def checker(nuggets, packs):

    # First get the values out of `packs` for convenience.
    x, y, z = packs[0], packs[1], packs[2]

    # Check the truth of the equation for every
    # permutation.
    for a in range(nuggets):
        for b in range(nuggets):
            for c in range(nuggets):
                if (x*a) + (y*b) + (z*c) == nuggets:
                    return True

def do():
    # get pack sizes
    packs = []
    while len(packs) < 3:
        usrin = raw_input('Enter a pack size: ')
        try:
            if int(usrin) > 1:
                if not int(usrin) in packs:
                    packs.append(int(usrin))
                else:
                    print '// You already entered', usrin
            else:
                print '...that\'s greater than one??'
        except:
            print 'Huh?...'

    # Check every number that's less than 200 to find the
    # highest number that can not be purchased evenly.
    tally = 200
    while tally:
        tally -= 1
        if not checker(tally, packs):
            return str(tally)


print '''
    #######################################
    #>   Welcome to MuckNugget Checker   <#
    #######################################
'''
bye_message = '''
    = = = = = = = = = =
    |    God Bless    |
    = = = = = = = = = =
'''
loop = True
while loop:
    # This print statement can not run until its call to `do()` has
    # returned. The `do()` function will print its input prompts
    # before it returns and allows this to print.
    print '''
    The greatest number below 200 that can
    not be purchased in the pack sizes you
    have entered is ''' +do()+ '.\n'

    if raw_input('Press Enter to continue.\nAnything else to quit. '):
        print bye_message
        loop = False
    else:
        print '\n    Let\'s go again...\n'