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