#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define rep1(i,n) for(int i=1;i<=(int)(n);i++)
#define fs first
#define sc second
typedef vector<ll> vl;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<char> vc;
typedef vector<tuple<ll,ll>> vtl;
typedef pair<ll, ll> l_l;
#define EPS (1e-7)
#define INF (1e9)
#define PI (acos(-1))

void solve(){
    //abc120c
    string s;
    cin>>s;
    ll ans,minr,mini;
    rep(i,n){
      if(s[i]=='0')minr++;
      else mini++;
    }
  ans=min(minr,mini);
    cout<<ans;
}

int main(){
    cout<<std::fixed<<std::setprecision(10);
    ios::sync_with_stdio(false);
    cin.tie(0);
    solve();
}