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 C (GCC 5.4.1) (judge verdict: Wrong Answer)

// B - Palindrome-philia
#include <stdio.h>
#include <string.h>

int main(void){
    char s[101], s1[51], s2[51];
    scanf("%s", s);
    int len=strlen(s)-1;
    //printf("len : %d\n", len);
    if(len+1==1){puts("0"); return 0;}
    if(len+1==2){puts("1"); return 0;}
    int halflen;

    if(len%2==0)halflen=len/2;
    else halflen=len/2+1;

    for(int i=0; i<=halflen; i++){
        s1[i]=s[i];
        s2[i]=s[len-i];   
    }
    s1[halflen]='\0', s2[halflen]='\0';
    int cnt=0;
    for(int i=0; s1[i]!='\0' && s2[i]!='\0'; i++){
        if(s1[i]!=s2[i]){
            s1[i]=s2[i];
            cnt++;
        }   
    }
    //printf("s1 : %s, s2 : %s\n", s1, s2);
    printf("%d\n", cnt);
    return 0;
}