https://jsfiddle.net/k7we6rv2

kamoku.js

const btn = $('#btn');
const mixtanisuu = $('#mixtanisuu');
const mixkamoku = $('#mixkamoku');
btn.click( () => {
  const paragraph = document.createElement('p');
  paragraph.classList.add('kamoku');
  const text = document.createTextNode(document.getElementById('kamoku').value);
  paragraph.appendChild(text);
  mixkamoku.append(paragraph);
  
  let sum = 0;
  $('.kamoku').each(function() {
  	sum += parseInt(this.textContent);
  });
  mixtanisuu.text(sum);
});