ll@n,@k,@a[n],z=0,s=0;
Heap<ll>q;
q.walloc(k);
rrep(i,n){
	if(i&1)z>?=s+a[i];
	s+=q.push(a[i]);
	if(i<=n-k)s-=q.pop();
}
wt(z);