($N,$M)=glob<>;
@D=sort{$a-$b}<>;
$\=9e9;
for(0..$M-$N){
	if($D[$_]<=0&&0<=$D[$_+$N-1]){
		$\-=$-=$\-($D[$_+$N-1]*2-$D[$_]);
		$\-=$-=$\-($D[$_+$N-1]-$D[$_]*2);
	}elsif($D[$_]<=0&&$D[$_+$N-1]<=0){
		$\-=$-=$\-(-$D[$_]);
	}elsif($D[$_]>=0&&$D[$_+$N-1]>=0){
		$\-=$-=$\-$D[$_+$N-1];
	}
}
print