'use strict';

const input = require("fs").readFileSync("/dev/stdin", "utf8");
const list = input.trim().split('');

const halfLength = Math.floor(list.length / 2);

let hugCount = 0;
for (let i = 0; i < halfLength; i++) {
    const head = list[i].trim();
    const tail = list[list.length - i - 1].trim();
    if (head !== tail) {
        hugCount++;
    }
}

console.log(hugCount);
