#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;
}