#include <iostream>
#include <string>
using namespace std;

int n;
string s;
int prefix_sum[51][2];
int values[51][2];

int main(){
    cin >> s;
    n = (int)s.size();
    s = 'a' + s;
    int num_1 = 0;
    for (int i = 1;i <= n;i++){
        if (s[i] == '1'){
            num_1++;
        }
        prefix_sum[i][0] = prefix_sum[i - 1][0];
        prefix_sum[i][1] = prefix_sum[i - 1][1];
        prefix_sum[i][s[i] - '0']++;
    }
    int ans = num_1;
    for (int i = 1;i <= n;i++){
        values[i][0] = prefix_sum[i - 1][1] - prefix_sum[i - 1][0];
        values[i][1] = prefix_sum[n][1] - prefix_sum[i][1] + prefix_sum[i][0];
    }
    int min_val = 1e9;
    for (int i = n;i >= 1;i--){
        ans = min(ans, values[i][0] + min_val);
        min_val = min(min_val, values[i][1]);
    }
    cout << ans << '\n';
    return 0;
}