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 Rust (1.42.0) (judge verdict: Accepted)

#![allow(non_snake_case)]
#![allow(unused_imports)]
use proconio::input;
use std::collections::HashMap;
use std::collections::VecDeque;
use std::cmp::max;
use std::cmp::min;


fn main() {
    input! {
        S: String,
    }

    // 文字列を両端から見ていってカウントしていく
    let mut ans = 0i64;

    // Sの長さが奇数でも偶数でも、左からS.len()文字を見ればOK
    for i in 0..S.len() / 2 {
        if &S[i..i + 1] != &S[S.len() - 1 - i..S.len() - 1 - i + 1] {
            ans += 1;
        }
    }

    println!("{}", ans);
}