#include <bits/stdc++.h>
using namespace std;
int main(){
    /*
    * ABBA -> dp[0] = 0, dp[1] = 0
    * ABCA -> dp[0] = 1, dp[1] = 1
    * ABCD -> dp[0] = 1, dp[1] = 2
    * ABBC -> dp[0] = 0, dp[1] = 2
    */
   /*
   * ABA -> dp[0] = 0, dp[1] = 0
   * ABC -> dp[0] = 0, dp[1] = 1
   * AAB -> dp[0] = 0, dp[1] = 1
   * AAA -> dp[-] = 0, dp[1] =0 0
   */
   string s; cin >> s;
   if(s.size()==2){
    cout << !(s[0]==s[1]) << "\n";
   }
   int center = s.size()/2;
   int dp[(s.size()+1)/2];
   for(auto & i : dp)i = 0;
   int lp = center-3, rp=center+2;
   if(s.size()%2==0){
    if(s[center]==s[center-1])dp[0] = 0;
    else dp[0]=1;
    if(s[center-2]!=s[center+1])dp[1] =2;
    else dp[1] = dp[0];
   }else if(s.size()%2==1){
    dp[0] = 0;
    if(s[center-1]==s[center+1])dp[1]=0;
    else dp[1] = 1;
    lp=center-2;
    rp=center+2;
   }
   while(lp>=0){
    if(s[lp]==s[rp]){
        dp[center-lp]=dp[center-lp-1];
    }else{
        if(s[lp+1] != s[rp-1]){
            dp[rp-center]=dp[rp-center-2]+1;
        }else{
            dp[rp-center]=dp[rp-center-2]+2;
        }
    }
    lp--; rp++;
   }
   cout << dp[center-(s.size()%2==0)] << "\n";
}