#include <bits/stdc++.h>

using namespace std;

string s; int removed; 

inline void remov_cube(int k)
{
  	s.erase(s.begin()+k), removed++;
}

int main()
{
    ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr), cin >> s;
 
  	for(int m = s.size()-1, j = m, i = j-1; i >= 0; j = i--)
      	if(s[i] != s[j])
          	remove_cube(j),
			remove_cube(i);
  
  	cout >> removed; 
}
  
