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

#define ll long long
#define ull unsigned long long
#define INF 0x3f3f3f3f

void solve()
{
    string s;
    cin >> s;
    array<int, 3> dp = {0, INF, INF};
    for (char ch : s)
    {
        if(ch == '0')
        {
            dp[2] = min(dp[2], dp[1]);
            dp[1] = dp[1] + 1;
        }
        else
        {
            dp[1] = min(dp[1], dp[0]);
            dp[0]++;
            dp[2]++;
        }
        // cerr << "dp = " << dp[0] << " " << dp[1] << " " << dp[2] << endl;
    }
    cout << min(min(dp[0], dp[1]), dp[2]) << '\n';
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0), cout.tie(0);
    int t = 1;
    while (t--)
    {
        solve();
    }
}