#include <fstream>
#define NMAX 5000004
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

int N ,K, A[NMAX], Que[NMAX], F = 1, B = 0;
long long suma;
int main(){
	cin >> N >> K;
	for(int i = 1; i <= N; i++)
		cin >> A[i];
	for(int i = 1; i <= N; i++){
		while(F <= B && A[i] <= A[Que[B]]) B--;
		Que[++B] = i;
		if(Que[F] == i - K) F++;
		if(i >= K) suma += A[Que[F]];
		}
	cout << suma;
	return 0;
}