I need the script to give me as a result the line of S12 as the lowest column3 value

I presume you actually meant you want the later line in the event of ties. (Upd: No, I don't think that's what you meant. I don't understand what you do want, so I can't offer another solution. )

$_ = <>;
my @fields = split;
my $lowest = my $highest = $fields[2];

while (<>) {
   my @fields = split;
   if ($fields[2] <= $lowest) {
      $lowest = $fields[2];
   }
   if ($fields[2] >= $highest) {
      $highest = $fields[2];
   }
}

print("$lowest\n");
print("$highest\n");
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