#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);
}