#!/usr/bin/env python3

def tokenize(string):
    # Splits string into list of tokens
    string = string.replace('(', ' ( ')
    string = string.replace(')', ' ) ')
    return string.split()

def find_matching_paren_offset(tokens):
    # Return index for first unmatched close parentheses.
    stack = []
    for i, token in enumerate(tokens):
        if token == '(':
            stack.append(token)
        elif token == ')':
            if len(stack) == 0:
                return i
            else:
                stack.pop()

def create_ast(tokens):
    ast = []
    i = 0
    while i < len(tokens):
        token = tokens[i]
        if token == '(':
            i += 1 # advance index to token after open paren
            end_paren_idx = find_matching_paren_offset(tokens[i:]) + i
            ast.append(create_ast(tokens[i : end_paren_idx]))
            i = end_paren_idx + 1 # update index to token after close paren
        else:
            if token.isdigit():
                token = int(token)
            ast.append(token)
            i += 1
    return ast

def parse(string):
    assert string.startswith('(') and string.endswith(')')
    return create_ast(tokenize(string[1:-1]))

def evaluate(ast):
    return ast

def test():
    assert parse('(+ 20 30)') == ['+', 20, 30]
    assert parse('(+ (* 2 3) 4)') == ['+', ['*', 2, 3], 4]
    assert parse('(- 3 (* 4 5))') == ['-', 3, ['*', 4, 5]]
    assert parse('(+ (* 2 3) (- 6 4))') == ['+', ['*', 2, 3], ['-', 6, 4]]
    assert parse('(first (list 1 (+ 2 3) 9))') == ['first', ['list', 1, ['+', 2, 3], 9]]

if __name__ == '__main__':
    test()
    while True:
        line = input('> ')
        print(evaluate(parse(line)))