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

using i64 = long long;

int main() {
    cin.tie(nullptr)->sync_with_stdio(false);

    auto solve = [&]() {
        string s;
        cin >> s;

        vector<int> dp(3);

        for (auto ch : s) {
            if (ch == '0') {
                dp[1] = min(dp[1] + 1, dp[0]);
            } else {
                dp[0]++;
                dp[2] = min(dp[2] + 1, dp[1]);
            }
        }

        cout << dp[2] << '\n';
    };
    
    solve();
    
    return 0;
}