# username = input('username: ')
# print('welome to', username + '.')
# print('welcome to ' + username + '.')
# print('welcome to %s.' % username)
# n = input('number: ')
# print(n)
# print(int(n) + 10)
# print(n + str(10))
# print(n, str(10))
# print(n, str(10), sep='')
# print(n, str(10), sep=' ')
# print(n + str(10) + str(20))
# print(n,10)
# # print(n,10,sep='')
# alist = [10, 'gzc', [20, 50]]
# blist = alist
# blist[-1] = 60
# blist.append(90)
# print(blist, alist)
