function main(input) {
    const reverse = input.split("").reverse().join("")
    const size = input.split("").length
    let count = 0

    for (let i=0; i< size/2; i++) {
      let a = input.split("")[i]
      let b = reverse.split("")[i]
      console.log(`i=${i}, a=${a} ${typeof a}, b=${b} ${typeof b}, compare=${a===b}`)
      if (a !== b) {
        count = count + 1
      }
    }
    console.log(count)
}
main(require('fs').readFileSync('/dev/stdin', 'utf8'));
