function Main(input) {
  var string2 = input
  .split('')
  .reverse()
  .join('');

var count = 0;

for (i = 0; i < string2.length; i++) {
  if (input[i] !== string2[i]) {
    count++;
  }
}

console.log(count);
}
Main(require('fs').readFileSync('/dev/stdin', 'utf8'));