script let mean = 0 let num = 0 let i = 0 while i = 20 num += i i++ mean=numi-1 documentwrite1~20之间的数的平均值为$mean script帮我优化一下

<script>
    let num = 0;
    for (let i = 1; i <= 20; i++) {
        num += i;
    }
    const mean = num / 20;
    document.write(`1~20之间的数的平均值为${mean}`);
</script>