#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
#define MAXIM 5000010
int v[MAXIM], deque[MAXIM];

int main()
{
	int n, k, back = 0, front = 1;
	in >> n >> k;
	long long sum = 0;
	for (int i = 1; i <= n; i++) in >> v[i];
	for (int i = 1; i <= n; i++)
	{
		while (front <= back && v[i] <= v[deque[back]]) back--;
		deque[++back] = i;
		if (deque[front] == i - k) front++;
		if (i >= k) sum += (long long)v[deque[front]];
	}
	out << sum;
	return 0;
}