[스택 - 4949번] 균형잡힌 세상

while True:
    n = input()
    stack = []

    if n == ".":
        break

    for i in n:
        if i == '[' or i == '(':
            stack.append(i)
        elif i == ']':
            if len(stack) != 0 and stack[-1] == '[':
                stack.pop()
            else:
                stack.append(i)
                break
        elif i == ')':
            if len(stack) != 0 and stack[-1] == "(":
                stack.pop()
            else:
                stack.append(i)
                break
    if len(stack) == 0:
        print('yes')
    else:
        print("no")