#include <iostream>
#include <algorithm>
#include <iterator>
#include <math.h>
#include <vector>
#include <set>
#include <map>
using namespace std;
vector<long long>v;
long long n, t, x, y, z, c;
int main() {
string s;
cin >> s;
c = z =0;
x = 0;
for (int i = 0; i < s.size(); i++){
if (s[i] == '1'){
if (z == 1 && x) c++;
z = 0;
c++;
x = 1;
}
else z++;
}
cout << c;
return 0;
}