include<bits/stdc++.h>
using namespace std;
int main(){
  string S;
  cin>>S;
  N = S.size()
  int cntred = 0; 
  int cntblue = 0;
  for(int i = 0;i<N;i++){
    if(S.at(i) =='1'){
      cntblue++;
    }
    else{
      cntred++;
    }
  }
  if(cntred=>cntblue){
    cout<<cntblue;
  }
  else{
    cout<<cntred;
  }
}