having trouble with user-input addition

javascript newbie here. I was trying to add 2 numbers via user input but the code returns a NaN warning in the console. I know other methods to do this but i wanted to it with the ES6 Features.

//HTML

<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <form>
        <input type="number" name="num1" id="num1">
        <input type="number" name="num2" id="num2">
        <button type="submit" value="+">+</button>
        <input type="number" name="num3" id="num3">
    </form>
    <script src="calculator.js"></script>
</body>
</html>


//JAVASCRIPT
const num1 = parseInt(document.querySelector('#num1').value);
const num2 = parseInt(document.querySelector('#num2').value);
const num3 =Number(document.querySelector('#num3').value);
const form = document.querySelector('form');


form.addEventListener('submit', e =>{
    e.preventDefault();

    const c = num1 + num2;
    form.num3.value = c;
});