#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    string S;
    cin >> S;
    S += '1';
    reverse(S.begin(), S.end());
    long long cnt = 0, ans = 0;
    for(int i=1; i<S.length(); i++) {
        if(S[i-1] == '1' && S[i] == '1') {
            S[i] = 'x';
            ans += cnt;
        }
        cnt += (S[i] == '0');
    }
    cout << ans << endl;
}