#include<iostream>
#include<fstream>
#define max_N 5000005

using namespace std;

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

int V[max_N], Deque[max_N], Front, Back, i, K, N;
long long Sum;

int main()
{
	fin >> N >> K;
	for(i = 1; i <= N; i ++)
		fin >> V[i];
	
	Front = 1, Back = 0;
	
	for(i = 1; i <= N; i ++)
	{
		while(V[i] <= V[Deque[Back]] && Back >= Front) Back --;
		Deque[++Back] = i;
		if(Deque[Front] == i - K)
			Front ++;
		if(i >= K)
			Sum += V[Deque[Front]];
	}
	fout << Sum;
	return 0;
}