fn main() {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).unwrap();
    let mut s = s.trim().bytes().collect::<Vec<_>>();
    let mut ans = 0;
    while s.len() > 0 {
        if *s.last().unwrap() == b'0' {
            s.pop();
        } else {
            let len = s.len();
            if len == 1 || s[len - 2] == b'0' {
                ans += 1;
                s.pop();
            } else {
                ans += 1;
                while s.last().map_or(false, |p| *p == b'1') {
                    s.pop();
                }
                s.pop();
                s.push(b'1');
            }
        }
    }
    println!("{}", ans);
}