my @pos;

my $start = index($str, 'M');

while ($start != -1) {
	my $pos;
	my $i = 0;
	
	1 while ($pos = index($str, 'M', $start + $i)) == $start + $i++;
	
	push @pos, [$start, $start + $i-2];
	
	$start = $pos;
}
##</code><code>##

my $i = 1;
    
$i++ while ($pos = index($str, 'M', $start + $i)) == $start + $i;
    
push @pos, [$start, $start + $i-1];