def checkio(expression):
    LEFT='([{'
    RIGHT=')]}'
    PAIR_ROUND='()'
    PAIR_SQUARE='[]'
    PAIR_CURLY='{}'
    l_bracket=[]
    for i in expression:
        if i in LEFT:
            l_bracket.append(i)
        if i in RIGHT:
            if not l_bracket: return False
            elif i in PAIR_ROUND and l_bracket[-1] in PAIR_ROUND:
                del l_bracket[-1]
            elif i in PAIR_SQUARE and l_bracket[-1] in PAIR_SQUARE:
                del l_bracket[-1]
            elif i in PAIR_CURLY and l_bracket[-1] in PAIR_CURLY:
                del l_bracket[-1]
            else: return False
    if not l_bracket: return True
    return False