#include <iostream>
#include <fstream>

using namespace std;

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

int n, k;
int a[5000010], deque[5000010];
long long s;

int main()
{
	fin >> n >> k;
	for (int i = 0; i < n; i++)
	{
		fin >> a[i];
	}
	int front = 0;
	int back = -1;

	for (int i = 0; i < n; i++)
	{ 
		while (front <= back && a[i] <= a[deque[back]]) 
			back--;

		deque[++back] = i;

		if (deque[front] == i - k) front++;

		if (i >= k - 1) s += a[deque[front]];
	}

	fout << s;

	return 0;
}