If you are looping through using an array for each of the values you mention, you could do something like this:

@array = ('1ST','10ST','101ST');
foreach (@array) {
   ($start,$end) = m/(.*)(.{2})/o;
   print "start = $start\nend = $end\n\n";
}
[download]

That would give you two values, upon which further processing would be possible.