function solve () {
  document.querySelector('button').addEventListener('click', register)
  let list = Array.from(document.querySelectorAll('li'))
  let input = document.querySelector('input')

  function register () {
    let index = input.value.toLowerCase().charCodeAt(0) - 97
    let name = input.value[0].toUpperCase() + input.value.slice(1).toLowerCase()
    list[index].textContent = list[index].textContent
      .split(', ')
      .filter(x => x)
      .concat(name)
      .join(', ')
  }
}