#include <bits/stdc++.h>
using namespace std;
#define maxn 5000010

ifstream fin("deque.in");
ofstream fout("deque.out");

int N, K, i;
int A[maxn], Deque[maxn];
int Front, Back;
long long suma;

int main()
{

	fin>>N>>K;
	for (i = 1; i <= N; i++){
		fin>>A[i];
	}

	Front = 1, Back = 0; 

	for (int 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){
		    suma += A[ Deque[Front]]; 
		} 	
	}

	fout<<suma;

}