#include <bits/stdc++.h>

using namespace std;

using i64 = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    string s;
    cin >> s;

    int n = s.size();
    int l = n, r = 0;
    for (int i = 0;i < n;i ++){
        if (s[i] == '1'){
            l = min(l, i);
            r = i;
        }
    }
    if (l == n){
        cout << 0;
    }else{
        int cnt = 0, ans = 0;
        for (int i = l;i <= r;i ++){
            if (s[i] == '0'){
                cnt ++;
            }else{
                if (cnt) ans ++;
                cnt = 0;
            }
        }
        cout << ans;
    }

    return 0;
}