#![allow(non_snake_case)]

use proconio::input;
use proconio::marker::Chars;

fn main() {
    input! {
        S: Chars,
    }
    let N = S.len();

    enum State {
        Start,
        NextOne,
    }
    use State::*;

    let mut ans = 0usize;
    let mut state = State::Start;
    let mut right = N;
    for i in (0 .. N).rev() {
        match state {
            Start => {
                if S[i] == '0' {
                    // none
                } else {
                    state = NextOne;
                }
            }
            NEXT_ONE => {
                if S[i] == '0' {
                    right -= 1;
                    state = Start;
                } else {
                    right -= 2;
                    ans += right - i;
                    state = Start;
                }
            }
        }
    }

    println!("{ans}");
}