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

template<typename T>
vector<pair<T,long long>> RLE(vector<T> &A){
    if(A.size() == 0) return {};
    vector<pair<T,long long>> ret;
    T back = A.at(0);
    long long streak = 1;
    for(int i=1; i<A.size(); i++){
        if(back == A.at(i)) streak++;
        else{
            ret.push_back({back,streak});
            back = A.at(i); streak = 1;
        }
    }
    ret.push_back({back,streak});
    return ret;
}
vector<pair<char,long long>> RLE(string &s){
    if(s.size() == 0) return {};
    vector<pair<char,long long>> ret;
    char back = s.at(0);
    long long streak = 1;
    for(int i=1; i<s.size(); i++){
        if(back == s.at(i)) streak++;
        else{
            ret.push_back({back,streak});
            back = s.at(i); streak = 1;
        }
    }
    ret.push_back({back,streak});
    return ret;
}

int main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    string s; cin >> s;
    auto S = RLE(s);
    int bring = 0;
    long long answer = 0;
    for(auto &[c,len] : S){
        if(c == '1') bring += len;
        else{
            bring -= bring%2;
            answer += len*(bring/2);
        }
    }
    cout << answer << endl;
}