#include<stdlib.h>
#include<stdio.h>
#include<fstream>
#include<string.h>
#include<deque>
#include<algorithm>
using namespace std;
deque <int> D;
long n, k, i, s, v[5000010],front,back;

int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	f >> n >> k;
	for (i = 1;i <= n;i++)
	{
		f >> v[i];
	}

	for (i = 1;i <= n;i++)
	{
		while ((D.size() != 0) && (v[i] <= v[D.back()]))
			D.pop_back();
		D.push_back(i);
		
		if (i >= k)
		{
			s = s + v[D.front()];
			if (((D.size() != 0) && (i - D.front() >= k - 1)))
				D.pop_front();
		}
	}
	g << s;
	return 0;
}