#include <iostream>
#include <fstream>

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

long long s;
int v[5000100], d[5000100], n, k, i, p, u;

int main()
{
	f >> n >> k;
	for (i = 1; i <= n; i++)
		f >> v[i];
	p = 1;
	u = 1;
	d[p] = 1;
	for (i = 2; i <= n; i++)
	{
		while (v[i] <= v[d[u]] && p <= u)
			u--;
		d[++u] = i;
		if (i - d[p] == k)
			p++;
		if (i >= k)
			s += v[d[p]];
	}
	g << s;
	return 0;
}