use std::io::*;
use std::str::FromStr;

fn read<T: FromStr>() -> T {
    let stdin = stdin();
    let stdin = stdin.lock();
    let token: String = stdin
        .bytes()
        .map(|c| c.expect("filed to read char") as char)
        .skip_while(|c| c.is_whitespace())
        .take_while(|c| !c.is_whitespace())
        .collect();
    token.parse().ok().expect("failed to parse token")
}

fn main() {
    let _n:usize = read();
    let s:String = read();
    let mut red = 0;
    let mut blue = 0;
    for i in s.chars() {
        if i == '0' {
            red += 1;
        } else {
            blue += 1;
        }
    }
    println!("{}", 2 * std::cmp::min(red, blue));
}