Is there a selector for first|last|n-item in a row with flex-wrap: wrap;?

Question

comrades.

I need to show a list of few elements with unknown width and number of elements, there a separators between items also. It can be few rows, or can not to be.

I use a flexboxed <ul> with flex-wrap and make separators with <li> `s border-left. I need to hide separators of first item of each row if row was wrapped to few rows.

ul {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}
li {
  flex: 0 0 auto;
  border-left: 1px solid red;
}
li:first-child { /* here i need something like ul:flex-row li:first-child */
  border-left: none;
}

html
<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
  <li>Item 4</li>
  <li>Item 5</li>
</ul>

Does there exist the solution of this task with css?
Or only thing i can use is js, like offset().top changes of <li>s parsing and adding modifier-classname?

Thanks ahead.