while(<>)
	%HoA=();
	next unless /^ATOM\b/;
	@split_atom_line=split(/\s+/, $_);
	$chain=$split_atom_line[4];
	$position=$split_atom_line[5];
	$Zcoordinate=$split_atom_line[8];

	if (not exists $HoA{$chain} or $position < $HoA{$chain}[0])
	{
		$HoA{$chain} = [$position, $Zcoordinate];
	}
	
	
	for $key ( keys %HoA ) {
    print "$key: $HoA{$key}[0]\n"; }
}