($n,$k,@p)=glob<>."0 ".<>;
@p[$a,$b]=@p[$b=$a+$k,$a],push@z,"\n$a $b"while($a)=grep$p[$_]>$p[$_+$k],1..$n-$k;
print grep($p[$_]-$_,1..$n)?-1:(@z+0,@z)