import sys
def dis(a,z):
    # 计算从a变到z需要的最小操作次数
    dis1 = abs(ord(a)-ord(z))
    if dis1 > 13:
        dis1 = 26-dis1
    return dis1
# print(dis('a','g'))

s = input()
l = len(s)
su = 0
for i in range(l//2):
    j = l-1-i
    if s[i]!=s[j]:
        su+=dis(s[i],s[j])
print(su)