#include <bits/stdc++.h>

using i64 = long long;
using u64 = unsigned long long;

constexpr int inf = 1E9;

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

    std::string s;
    std::cin >> s;

    std::array <int, 3> dp{};
    for(auto c : s) {
        if(c == '0') {
            dp[1] = std::min(dp[0], dp[1] + 1);
        } else {
            dp[0]++;
            dp[2] = std::min(dp[1], dp[2] + 1);
        }
    }

    std::cout << dp[2] << '\n';

    return 0;
}