#include <iostream>
#include <algorithm>
#include <string>

void solve() {
    std::string s;
    std::cin >> s;
    int n = s.length();

    std::reverse(s.begin(), s.end());

    int ans = 0, carry = 0;
    for (int i = 0; i < n; ++i) {
        if (s[i] == '0') {
            s[i] += carry;
            carry = 0;
        }

        if (s[i] == '1' && !carry) {
            ++ans;
            if (i + 1 < n && s[i + 1] == '1') carry = 1;
        }
    }
    ans += carry;

    std::cout << ans << "\n";
}

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

    solve();

    return 0;
}