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 (1.15.1) (judge verdict: Runtime Error)

use std::io::Read;

fn main() {
    let mut buf = String::new();
    std::io::stdin().read_line(&mut buf).unwrap();
    let mut iter = buf.split_whitespace();
    let s = iter.next().unwrap().as_bytes();
    let mut head:usize = 0;
    let mut tail:usize = s.len()-1;
    let mut ans = 0 ;
    while head <= tail {
        if s[head] != s[tail] {
            ans += 1;
        }
        head += 1;
        tail -= 1;
    }
    println!("{}", ans);
}