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


int main() {
    string s;
    cin >> s;
    while (!s.empty() && ~s.back() & 1) s.pop_back();
    reverse(s.begin(), s.end());
    while (!s.empty() && ~s.back() & 1) s.pop_back();
    if (!s.empty()) {
        int n = s.size();
        vector<array<int, 2>> pre(n + 1), suf(n + 2);
        pre[0][0] = pre[0][1] = 0;
        suf[n][0] = suf[n][1] = 0;
        for (int i = 1; i <= n; i++) {
            pre[i][0] = pre[i - 1][0] + (s[i - 1] == '0');
            pre[i][1] = pre[i - 1][1] + (s[i - 1] == '1');
        }
        for (int i = n; i >= 1; i--) {
            suf[i][0] = suf[i + 1][0] + (s[i - 1] == '0');
            suf[i][1] = suf[i + 1][1] + (s[i - 1] == '1');
        }
        int res = n;
        for (int i = 1; i <= n; i++) {
            res = min(res, pre[i][0] + suf[i + 1][1]);
            res = min(res, pre[i][1] + suf[i + 1][0]);
        }
        cout << res;
    } else {
        cout << 0;
    }

    return 0;
}