#include<iostream>
#include <fstream>
using namespace std;
#define maxn 5000010
ifstream fin("deque.in");
ofstream fout("deque.out");

int vec[maxn], deque[maxn];
int front, back;
int n, k;
int sum;

int main(){
	fin >> n;
	fin >> k;
	for(int i = 1; i <= n; i++){
		fin >> vec[i];
	}

	int front = 1;
	int back = 0;
	for(int i = 1; i <= n; i++){
		while(front <= back && vec[i] <= vec[deque[back]]){
			back--;
		}
		deque[++back] = i;
		if(deque[front]==i-k){
			front++;
		}
		if(i >= k){
			sum += vec[deque[front]];
		}
	}
	fout << sum;
	return 0;
}