#include 

using namespace std;

int main(void) {
    string s;
    cin >> s;

    int result = 0;
    int temp = 0;

    for(auto c = s.begin(); c != s.end(); c++)
        result += (temp = (*c == '1' ? temp + 1 : 0));

    cout << result << endl;

    return 0;
}