# coding: utf-8

# submission # - User: herp_sy

# https://atcoder.jp/contests/

#

# lang: Python3 (3.4.3)



import math

import statistics

import numpy as np

import queue



s = eval(input())

cnt = 0



for i in range(len(s) // 2):

  if s[i] != s[len(s) - 1 - i]:

    cnt += 1



print(cnt)
# coding: utf-8

# submission # - User: herp_sy

# https://atcoder.jp/contests/

#

# lang: Python3 (3.4.3)



s = eval(input())

cnt = 0



for i in range(len(s) // 2):

  if s[i] != s[len(s) - 1 - i]:

    cnt += 1



print(cnt)

# coding: utf-8
# submission # - User: herp_sy
# https://atcoder.jp/contests/
#
# lang: Python3 (3.4.3)
import math
import statistics
import numpy as np
import queue

s = eval(input())
cnt = 0
for i in range(len(s) // 2):
    if s[i] != s[len(s) - 1 - i]:
        cnt += 1
print(cnt)

# coding: utf-8
# submission # - User: herp_sy
# https://atcoder.jp/contests/
#
# lang: Python3 (3.4.3)
s = eval(input())
cnt = 0
for i in range(len(s) // 2):
    if s[i] != s[len(s) - 1 - i]:
        cnt += 1
print(cnt)

-import math -import statistics -import numpy as np -import queue -