($N,$K)=glob<>;
@a=glob<>;
for(0..$K-1){
	for($i=$_;$i<$N;$i+=$K){
		for($j=$i;$j<$N;$j+=$K){
			if($a[$i]>$a[$j]){
				++$%;
				@a[$i,$j]=@a[$j,$i]
			}
		}
	}
}
print@a~~@{[sort{$a-$b}@a]}?$%:-1