pro

function solve() {
  let input = document.getElementById('input').value

  let splittedText = input.split('.').filter(x => x !== "").map(y => y + ".")
  let output = document.getElementById('output')
  output.innerHTML = ""

  let paragraphNum = Math.ceil(splittedText.length / 3)

  for (let i = 0; i < paragraphNum; i++) {
    let finalString = sentence.splice(0, 3).join(", ")
    output.innerHTML += `<p>${finalString}</p>`
  }

}