import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        String s = in.next();
        int n = s.length();
        int left = 0;
        int right = n - 1;
        int result = 0;
        while (left < right) {
            char sLeft = s.charAt(left);
            char sRight = s.charAt(right);
            int nLeft = sLeft - 'a';
            int nRight = sRight - 'a';
            if (nLeft >= nRight) {
                int num1 = nLeft - nRight;
                int num2 = nRight + 26 - nLeft;
                if (num1 <= num2) {
                    result += num1;
                } else {
                    result += num2;
                }
            } else {
                int num1 = nRight - nLeft;
                int num2 = nLeft + 26 - nRight;
                if (num1 <= num2) {
                    result += num1;
                } else {
                    result += num2;
                }
            }
            left++;
            right--;
        }
        System.out.println(result);
    }
}