#include <iostream>
#include <fstream>

#define maxn 5000010

using namespace std;

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

int n, k;
int a[maxn], Deque[maxn];
int primul, ultimul;
long long s;

int main()
{
	int i;

	fin>>n>>k;

	for (i = 1; i <= n; i++)
        fin>>a[i];

	primul = 1;
	ultimul = 0;

	for (i = 1; i <= n; i++)
	{
		while (primul <= ultimul && a[i] <= a[ Deque[ultimul] ])
		    ultimul--;

		Deque[++ultimul] = i;

		if (Deque[primul] == i - k)
		    primul++;

		if (i >= k)
		    s = s + a[ Deque[primul]];
	}

	fout<<s;

	fin.close();
	fout.close();
	return 0;
}