#include<iostream>
using namespace std;
int main()
{
    string s;
    cin>>s;
    int tot1=0,tot2=0;
    for(int i=0;i<s.length();i++)
    {
        tot1+=s[i]==‘0‘;
        tot2+=s[i]==‘1‘;
    }
    cout<<min(tot1,tot2)<<endl;
    return 0;
}