#include <iostream>
#include <string>
#include <cmath>
using namespace std;

int main(){
    string s;
    int count = 0;
    if(cin>>s){
        for(int i = 0; i <s.length()/2; ++i){
            int count_min = min(abs(s[i] - s[s.length()-i-1]),26-abs(s[i] - s[s.length()-i-1]));
            count += count_min;
        }
        cout<<count<<endl;
    }
    return 0;
}