#include <bits/stdc++.h>

using i64 = 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;
}