Execute the break; in SCSS

I have some code.

Pug:

div(data-counter="100")

SCSS:

$start: 100;
$end: 20;

div:before {
  content: attr(data-counter);
  animation: countdown 10s steps(1, start) forwards;
}

@keyframes countdown {
  @for $i from 1 through $start { 
    @if $i == 50 {
      100% {
        content: 'Stop';
      }
    } @else {
      #{$i}% {
        content: '#{($start - $i)}';
      }
    }
  } 
}

The problem is that the counter counts from 100 and when it reaches 50, the counter would stop - 100% {content: 'Stop'; } And the animation would end (now it continues 49% {content: '51';} 100% {content: 'Stop';} 51% {content: '49';}).

Question: Is there something like break; for scss like in js?

codepen

P.S: @break; does not work as desired.

PPS: Same question in Russian.