#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k;
int a[5000010], deque[5000010];
int front, back;
long long sum;
int main()
{
	int i;
	f >> n >> k;
	for (i = 1; i <= n; i++)
		f >> a[i];
	front = 1;
	back = 1;
	for (i = 1; i <= n; i++)
	{
		while (front <= back && a[i] < a[deque[back]])
			back--;
		deque[++back] = i;
		if (deque[front] == i - k)
			front++;
		if (i >= k)
			sum += a[deque[front]];
	}
	g << sum;
}