#include <algorithm>
#include <iostream>
using namespace std;

int main() {
    string s;
    cin >> s;
    int cnt = 0;
    int s1, s2;
    for (int i = 0; i < s.size() / 2; i++) {
        if (s[i] != s[s.size() - 1 - i]) {
            if (s[i] > s[s.size() - 1 - i]) {
                s1 = 26 - (s[i] - s[s.size() - 1 - i]);
                s2 = s[i] - s[s.size() - 1 - i];
                cnt += min(s1, s2);
            }
            else {
                s1 = 26 - (s[s.size() - 1 - i] - s[i]);
                s2 = s[s.size() - 1 - i] - s[i];
                cnt += min(s1, s2);
            }
            // a b: 1 和 25
            // b a: 25 和 1
        }
    }
    cout << cnt;
}