#include<bits/stdc++.h>

using namespace std;

// #define int long long
#define endl '\n'

int f[55][5], len;
void solve() {
    string s;
    cin >> s;
    len = s.length();
    s = "*" + s;
    for(int i = 1; i <= len; i++) {
        if(s[i] == '0') {
            f[i][0] = f[i - 1][0];
            f[i][1] = min(f[i - 1][0], f[i - 1][1]) + 1;
            f[i][2] = min(f[i - 1][1], f[i - 1][2]);
        } else {
            f[i][0] = f[i - 1][0] + 1;
            f[i][1] = min(f[i - 1][0], f[i - 1][1]);
            f[i][2] = min(f[i - 1][1], f[i - 2][2]) + 1;
        }
    }
    cout << min(f[len][0], min(f[len][1], f[len][2]));
}

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

    int T = 1;
    // cin >> T;

    while (T--) {
        solve();
    }

    return 0;
}