fn main() {
    let mut n = String::new();
    std::io::stdin().read_line(&mut n).ok();
    let mut n = n.trim().chars().map(|c| c as usize - '0' as usize).collect::<Vec<_>>();

    let limit = n.len();
    let mut result = 0usize;
    let mut addval = 0usize;
    for i in 0..limit {
        if addval == 1 && n[i] == 1 {
            n[i] = 0;
        } else {
            n[i] = (n[i] + addval) % 2;
            addval = 0;
        }
        if i+1 < limit && n[i] == 1 && n[i+1] == 1 {
            result += 1;
            addval = 1;
            n[i] = 0;
        } else if n[i] == 1 {
            result += 1;
            n[i] = 0;
        }
    }
    println!("{}", result + addval);
}