#include<fstream>
#define nmax 5000001
using namespace std;
int n,k,V[nmax],coada[nmax],suma=0;
int main(){
	int head,tail;
	ifstream f("deque.in");
	ofstream g("deque.out");
	f>>n>>k;
	for(int i=1;i<=n;i++)
		f>>V[i];
	head=1;
	tail=0;
	for(int i=1;i<=n;i++){
		while(head<=tail&&V[i]<=V[coada[tail]])
			tail--;
		tail++;
		coada[tail]=i;
		if(coada[head]==i-k)
			head++;
		if(i>=k)
			suma=suma+V[coada[head]];
	}
	g<<suma;
	f.close();
	g.close();
	return 0;
}