Flex container width fit content width with flex-wrap: wrap?

Question

Here is an example:

.wrap {
  display: flex;
}

.wrap2 {
  padding: 4px;
  margin: 20px;
  outline: 1px dashed;
  display: flex;
  flex-wrap: wrap;
  max-width: 310px;
}

.box {
  width: 40px;
  height: 40px;
  outline: 1px solid;
}

<div class="wrap">
  <div class="wrap2">
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
    <div class="box"></div>
  </div>
</div>

And here is what I need:

I tried to wrap flex container with another flex, but it didnt work. Is there any CSS only solution, or i should use js to achive desired result?