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);
}
}