<form id="3nr">
  <p><input type="number" placeholder="Numri i pare..."></p>
  <p><input type="number" placeholder="Numri i dyte..."></p>
  <p><input type="number" placeholder="Numri i trete..."></p>
  <p>Numri me i vogel = <output name="min"></output></p>

</form>

        <script type="text/javascript">
    const form = document.querySelector('form')
const inputs = form.querySelectorAll('input[type="number"]')
const out = document.querySelector('output')

form.addEventListener('input', e => {
  out.value = Math.min(...Array.prototype.map.call(inputs, input => input.value))
}, false)
        </script>