#include <stdio.h>

#define max_n 5000010

    int N, K;
    int A[max_n], Deque[max_n];
    int Front, Back;
    long long Sum;
    
int main() {
    int i;
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	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;
}