import sys

import math

#a,b= map(int,input().split())

#li= [int(x) for x in input().split()]

a=eval(input())

b=len(a)

e=[]

count=0

if b%2==0:

  c=a[math.floor(b/2):]

  f=int(b/2)

  f+=1

else:

  b+=1

  c=a[math.floor(b/2):]

  f=int(b/2)

e = list(reversed(c))

d=list(a)

#print(str(d)+"  "+str(e))

for i in range(f-1):

  if d[i]==e[i]:

    continue

  else:

    count+=1

print(count)
import sys

import math

#a,b= map(int,input().split())

#li= [int(x) for x in input().split()]

a=eval(input())

count=0



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

  if a[i]==a[-i-1]:

    continue

  else:

    count+=1

print(count)

import sys
import math

# a,b= map(int,input().split())
# li= [int(x) for x in input().split()]
a = eval(input())
b = len(a)
e = []
count = 0
if b % 2 == 0:
    c = a[math.floor(b / 2) :]
    f = int(b / 2)
    f += 1
else:
    b += 1
    c = a[math.floor(b / 2) :]
    f = int(b / 2)
e = list(reversed(c))
d = list(a)
# print(str(d)+"  "+str(e))
for i in range(f - 1):
    if d[i] == e[i]:
        continue
    else:
        count += 1
print(count)

import sys
import math

# a,b= map(int,input().split())
# li= [int(x) for x in input().split()]
a = eval(input())
count = 0
for i in range(len(a) // 2):
    if a[i] == a[-i - 1]:
        continue
    else:
        count += 1
print(count)

-b = len(a) -e = [] -if b % 2 == 0: -    c = a[math.floor(b / 2) :] -    f = int(b / 2) -    f += 1 -else: -    b += 1 -    c = a[math.floor(b / 2) :] -    f = int(b / 2) -e = list(reversed(c)) -d = list(a) -# print(str(d)+"  "+str(e)) -for i in range(f - 1): -    if d[i] == e[i]: +for i in range(len(a) // 2): +    if a[i] == a[-i - 1]: