use proconio::{input, marker::Chars};
fn main() {
    input!{
        s: Chars
    }
    let mut cnt = 0;
    let mut ans = 0;
    let mut l = 0;
    for i in 0..s.len(){
        if s[i] == '0'{
            ans += cnt;
            l = 0
        }
        else{
            l += 1;
            if l&1==0{
                cnt += 1;
            }
        }
    }
    println!("{}",ans);
}