def trim(s):

  if len(s) >1:

    while s[0] == ' ' and s[-1] == ' ':

      s = s[1:-1]

    while s[0] == ' ' and s[-1] != ' ':

      s = s[1:]

    while s[0] != ' ' and s[-1] == ' ':

      s = s[:-1]

    print(s)

s = input('请输入字符串')

trim(s)