#include <stdio.h>
#include <stdlib.h>

#define MAXN 5000001

int v[MAXN];
int N,K;

////////////// QUEUE ///////////////////

typedef struct tagNode{
	int position;
	struct tagNode* next;
	struct tagNode* back;
}Node;

typedef struct tagQueue{
	Node *start;
	Node *end;
}Queue;

void initQueue(Queue *q)
{
	q->start = NULL;
	q->end = NULL;
}

void pushQueue(Queue *q, int pos)
{
	Node *aux = q->end;
	while( aux != NULL && v[pos] <= v[aux->position] )
		aux = aux->back;
		
	Node *new = malloc(sizeof(Node));
	new->position = pos;
	new->next = NULL;
	new->back = aux;
	q->end = new;
	
	if( aux == NULL ){
		q->start = new;
	}
	else{
		aux->next = new;
	}
}

int topQueue(Queue *q)
{
	return q->start->position;
}

void popQueue(Queue *q, int v)
{
	if( q->start->position != v )
		return;

	if( q->start->next == NULL){
		free(q->start);
		q->start = NULL;
		q->end = NULL;
	}
	else{		
		q->start = q->start->next;
		free(q->start->back);
		q->start->back = NULL;
	}
}

int isEmptyQueue(Queue *q)
{
	return q->start == NULL;
}

////////////////////////////////////////

int main(int argc, char* argv[])
{
	freopen("deque.in","r",stdin);
	freopen("deque.out","w",stdout);
	
	scanf("%d %d",&N,&K);
	
	int i;
	for(i=1;i<=N;i++)
		scanf("%d",&v[i]);
		
	Queue q;
	long long sum = 0;
	initQueue(&q);
	
	for(i=1;i<=K;i++)
		pushQueue(&q,i);
		
	sum += v[topQueue(&q)];
	
	for(i=K+1;i<=N;i++){
		popQueue(&q, i-K);
		pushQueue(&q, i);
		sum += v[topQueue(&q)];		
	}
	printf("%lld",sum);
	return 0;
}