using System;
using System.Collections.Generic;
public class Program {
    public static void Main() {
        string str = Console.ReadLine();

        //双指针
        int left = 0;
        int right = str.Length - 1;

        int totalOpCount = 0;

        while (left < right) {
            char leftChar = str[left];
            char rightChar = str[right];
            int leftPos = leftChar - 'a';
            int rightPos = rightChar - 'a';
			//计算两个字符之间的直接距离
            int directDistance = Math.Abs(leftPos - rightPos);
		  	//计算环绕距离并对比和直接距离的大小,选择出最小的那个
            int wrapAroundDistance = 26 - directDistance;
            int shortestDistance = Math.Min(directDistance, wrapAroundDistance);

            totalOpCount += shortestDistance;

            left++;
            right--;
        }
        Console.WriteLine(totalOpCount);
    }
    
}