#include <iostream>
#include <fstream>
#include<deque>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n, k;

deque<pair<int,int>>dq;

int main()
{
	f >> n >> k;
	long sum = 0;
	for (int i = 1; i <= n; i++)
	{
		int x;
		f >> x;
		while (!dq.empty() && x <= dq.back().first)
		{
			dq.pop_back();
		}
		dq.push_back({ x,i });
		while (!dq.empty() && dq.front().second <= i-k)
		{
			dq.pop_front();
		}
		if (i >= k)
		{
			sum = sum + dq.front().first;
		}
	}
	g << sum;
}