#pragma GCC optimize("Ofast")
#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef unsigned long long int ull;

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());
ll myRand(ll B) { return (ull)rng() % B; }

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    string s;
    cin >> s;
    int n = s.size();
    vector<vector<int>> dp(3, vector<int>(n + 1, 1e9));
    dp[0][0] = dp[1][0] = dp[2][0] = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < 3; ++j) {
            if (j == 1) {
                dp[j][i + 1] = min(dp[j][i + 1], dp[j][i] + (s[i] == '0'));
            } else {
                dp[j][i + 1] = min(dp[j][i + 1], dp[j][i] + (s[i] == '1'));
            }
        }
        dp[1][i + 1] = min(dp[1][i + 1], dp[0][i]);
        dp[2][i + 1] = min(dp[2][i + 1], dp[1][i]);
    }
    cout << dp[2][n] << endl;
}