Problem:
Score : 200 points

Problem Statement

Takahashi loves palindromes. Non-palindromic strings are unacceptable to him. Each time he hugs a string, he can change one of its characters to any character of his choice.

Given is a string S. Find the minimum number of hugs needed to make S palindromic.

Constraints

S is a string consisting of lowercase English letters.

The length of S is between 1 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

S

Output

Print the minimum number of hugs needed to make S palindromic.

Sample Input 1

redcoder

Sample Output 1

1

For example, we can change the fourth character to o and get a palindrome redooder.

Sample Input 2

vvvvvv

Sample Output 2

0

We might need no hugs at all.

Sample Input 3

abcdabc

Sample Output 3

2

Solution in Python (3.4.3) (judge verdict: Accepted)

# coding:utf-8

import sys
import math
import time
import numpy as np
import collections
from collections import deque
import queue
import copy

# 最大公約数
def gcd(m,n):
  x = max(m,n)
  y = min(m,n)
  if x%y == 0:
    return y
  else:
    while x%y != 0:
      z = x%y
      x = y
      y = z
    else:
      return z

# 幅優先探索(BFS)でスタート座標(x, y)からの最大距離返す
def bfs(SS, x, y, H, W):#入力(座標系(迷路), x, y, xの端, yの端)
  x_next = [0, 0, -1, 1]
  y_next = [1, -1, 0, 0]
  tempx = x
  tempy = y
  mlength = 0
  q = deque()
  xytuple = (x, y, 0)
  q.append(xytuple)


  while q:
    xytuple = q.popleft()
    SS[xytuple[0]][xytuple[1]] = "x" #探索した場所は探索できないようにする
    for i in range(4): #このforで上下左右を調べてる
      tempx = xytuple[0] + x_next[i]
      tempy = xytuple[1] + y_next[i]
      #print(tempx, tempy, xytuple[2])
      #print(S)
      if(0 <= tempx and tempx < H and 0 <= tempy and tempy < W and SS[tempx][tempy] == "."):
        temptuple = (tempx, tempy, xytuple[2]+1)
        SS[temptuple[0]][temptuple[1]] = "x" #探索した場所は探索できないようにする
        mlength = max(mlength, xytuple[2] +1)
        q.append(temptuple)
      #print(q)
  return mlength


#X = str(input()).split()
S = str(input())
s = []
#a = int(A[0])
# S = [[0 for i in range(W)] for j in range(H)]
cont=0


if(len(S)%2 == 0):
  for i in range(int(len(S)/2)):
    s.append(S[i])
  for i in range(int(len(S)/2)):
    s.append(s[int(len(S)/2)-1-i])
else:
  for i in range(int((len(S)-1)/2)+1):
    s.append(S[i])
  for i in range(int((len(S)-1)/2)):
    s.append(s[int((len(S)-1)/2)-1-i])

for i in range(len(S)):
  if(S[i]==s[i]):
    cont += 0
  else:
    cont+= 1

#print(S)
#S[2] = "a"
print(cont)



#print(ans)