#include <iostream>

int main(){
	std::string S;
  	std::sin>>S;
  	int count0=0,count1=0;
  	for(int i=0;i<S.size();++i){
		if(S[i]=='0'){
        	count0++;	
        }else{
        	count1++;
        }
    }
  std::cout<<std::min(count0,count1);
  return 0;
}