#include <stdio.h>
#define maxn 5000010

int N, K;
int A[maxn], Deque[maxn];
int Front, Back;
long long Sum;



int main(){
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);

	int i;

	scanf("%d %d ", &N, &K);



	for (i = 1; i <= N; i++)
		scanf("%d ", &A[i]);

	Front = 1, Back = 0;

	for (i = 1; i <= N; i++)	{

		while (Front <= Back && A[i] <= A[ Deque[Back] ]) Back--;
		Deque[++Back] = i;

		if (Deque[Front] == i-K) Front++;
		if (i >= K) Sum += A[ Deque[Front]];
	}
	printf("%lld\n", Sum);
	return 0;

}