# Process input
s = input()

# Algo
cnt = 0
for i in range(len(s)//2):
    chLeft = s[i]
    chRight = s[len(s)-i-1]
    ordL = ord(chLeft)
    ordR = ord(chRight)
    dis = abs(ordL-ordR)
    cnt += min(dis, 26-dis)

print(cnt)