format the text - js advanced DOM1 -ex

function solve() {
  const text = document.getElementById('input').value;
  const sentences = text.split('.');
  sentences.pop();
  let result = '';

  for (let i = 0; i < sentences.length; i += 3) {
    result += `<p>${sentences[i]}.`;
    if (sentences[i + 1] != undefined) {
      result += sentences[i + 1] + '.';
    }
    if (sentences[i + 2] != undefined) {
      result += sentences[i + 2] + '.';
    }
    result += '</p>'
  }

  document.getElementById('output').innerHTML = result;
}