fn main() {
    let input = std::env::args().skip(1).next().unwrap();
    let mut stack = Vec::with_capacity(input.len() / 4);
    for ch in input.chars() {
        match (ch, stack.last()) {
            ('}', Some(&'{')) | (']', Some(&'[')) | (')', Some(&'(')) => {
                stack.pop();
            }
            _ => stack.push(ch),
        }
    }
    let output: String = stack.iter().collect();
    println!("{}", output);
}