#include<bits/stdc++.h>
#include<bits/extc++.h>
#define time chrono::system_clock::now().time_since_epoch().count()
#define maxn 1000005
// #define int long long
using namespace std;
using namespace __gnu_pbds;
mt19937_64 rnd(time);

int read() {int x;cin>>x;return x;}

signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);

    return 0;
    string a;
    cin>>a;
    int n = a.length();
    a = "s" + a;
    int cnt1 = count(a.begin(), a.end(), '1');
    // cout<<"cnt1:"<<cnt1<<"\n";
    int inf = 1e9;
    vector f(n + 1, vector(2 * n * n + 1, inf));
    int bias = n * n;
    f[0][bias] = 0;
    for(int i = 0; i < n; i++) {
        vector g(n + 1, vector(2 * n * n, inf));
        for(int j = 0; j <= n; j++) {
            for(int k = 1; k <= 2 * n * n; k++) {
                if(f[j][k] != inf) {
                    g[j][k - j] = min(g[j][k - j], f[j][k] + (a[i + 1] != '0'));
                    g[j + 1][k + i - j] = min(g[j + 1][k + i - j], f[j][k] + (a[i + 1] != '1'));
                }
            }
        }
        f = g;
    }
    cout<<f[cnt1][bias] / 2;
    return 0;
}