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

using namespace std;

int main()
{
	ifstream in("deque.in");
	ofstream out("deque.out");

	int n, k;
	long long sum = 0;
	deque<int> d;
	int *vec;

	in >> n >> k;

	vec = new int[n];

	for(int i = 0 ; i < n ; i++)
	{
		in >> vec[i];
	}

	for(int i = 0 ; i < n ; i++)
	{
		while(d.empty() != true && vec[i] <= vec[d.back()])
		{
			d.pop_back();
		}

		d.push_back(i);

		if(d.front() == i - k)
		{
			d.pop_front();
		}

		if(i >= k - 1)
		{
			sum += vec[d.front()];
		}
	}
	out << sum << '\n';

	return 0;
}