#!/usr/bin/env python

from operator import add, sub

from random import randint, choice

ops = {'+': add, '-': sub}

MAXTRIES = 2

def doprob():

    op = choice('+-')

    nums = [ randint(1,10) for i in range(2) ]

    nums.sort(reverse=True)

    ans = ops[op](*nums)

    pr = '%d %s %s = ' % (nums[0], op, nums[1])

    oops = 0

    while True:

        try:

            if int(raw_input(pr)) == ans:##只有正确作答才跳出循环

                print 'correct'

                break

            if oops == MAXTRIES:##第二次给出正确答案，但是依然是这道题目

                print 'sorry... the answer is\n%s%d' % (pr, ans)

            else:

                print 'incorrect... try again'

                oops += 1

        except (KeyboardInterrupt,

                EOFError, ValueError):

            print 'invalid input... try again'

def main():

    while True:

        doprob()

        try:

            opt = raw_input('Again? [y] ').lower()

            if opt and opt[0] == 'n':

                break

        except (KeyboardInterrupt, EOFError):

            break

if __name__ == '__main__':

    main()