# -*- coding:utf-8 -*-

def trim(s):
    count = 0
    for n in s:
        if n == ' ':
            count = count + 1
        else:
            break
    s = s[count:]
    count = 0
    for n in s[-1:]:
        if n ==' ':
            count = count + 1
    s = s[:-count]

    return s

print(trim('hello   '))
print(trim('   hello'))
print(trim('   hello   '))
print(trim('   hello world   '))