#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int v[5000001], deque[5000001];
int  n, k, st, dr;
long long suma;
int main()
{
	f >> n >> k;
	for (int i = 1; i <= n; i++)
		f >> v[i];
	dr = 0;
	st = 1;
	for (int j = 1; j <= n; j++)
	{
		while (v[j] <= v[deque[dr]] && st <= dr )
			dr--;
		dr++;
		deque[dr] = j;
		if (deque[st] <= j - k)
			st++;
		if (j >= k)
			suma += v[deque[st]];
	}
	g << suma;
	return 0;
}