function healing(input, preparation) {
  if (!input || !preparation) {
    return input
  }
  if (typeof input !== "string" || typeof preparation !== "string") {
    return input
  }
  let collected = ""
  let chamber = []
  for (let i=0;i<input.length;i++) {
    chamber.push(input[i])
    for (let j=0;j<preparation.length;j++) {
      chamber.push(preparation[j])
    }
    for (let j=0;j<chamber.length-1;j++) {
      let a = chamber[j]
      chamber[j] = chamber[j+1]
      chamber[j+1] = a
    }
    collected += chamber[chamber.length-1]
    chamber = []
  }
  return collected
}
healing("self", "forgiveness") // "self"