function solve (arr) {
  let testedWords = arr.pop().split(' ')
  let searchedWord = testedWords[0]
  let parsedWord = testedWords[1]
  let result = ''
  let savedChar = ''

  let singleWord = arr[0]

  for (let j = 0; j < singleWord.length; j++) {
    let singelChar = singleWord[j]
    let charCode = singelChar.charCodeAt(0)

    if ((charCode > 99 && charCode <= 125) || charCode === 35) {
      let fromCharCode = String.fromCharCode(charCode - 3)
      result += fromCharCode
    } else {
      console.log('This is not the book you are looking for.')
      return
    }
  }

  result += savedChar
  let index = result.indexOf(searchedWord)

  while (index !== -1) {
    result = result.replace(searchedWord, parsedWord)
    index = result.indexOf(searchedWord)
  }

  console.log(result)
}