#include <iostream>
using namespace std;

int main() {
    string s;cin>>s;
    int l=0,r=s.size()-1;
    int c=0;
    while(l<r)
    {
        if(s[l]!=s[r]) 
        {
            int t=min(abs(s[l]-s[r]),26-abs(s[l]-s[r]));
            c+=t;
        }
        l++;
        r--;
    }
    cout<<c;
}