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

void solve()
{
    string s;
    cin >> s;
    int n = s.size();
    vector<vector<int>> dp(n, vector<int>(3, n));
    dp[0][s[0] - '0'] = 0;
    dp[0][!(s[0] - '0')] = 1;
    for (int i = 1; i < n; ++i)
    {
        if (s[i] == '1')
        {
            dp[i][0] = dp[i - 1][0] + 1;
            dp[i][1] = min(dp[i - 1][0], dp[i - 1][1]);
            dp[i][2] = min(dp[i - 1][2], dp[i - 1][1]) + 1;
        }
        else
        {
            dp[i][0] = dp[i - 1][0];
            dp[i][1] = dp[i - 1][1] + 1;
            dp[i][2] = min(dp[i - 1][1], dp[i - 1][2]);
        }
    }
    cout << min(dp[n - 1][1], dp[n - 1][2]);
    return;
}

int main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int T = 1;
    //cin >> T;
    while (T--) solve();
    return 0;
}