#include <iostream>
#include <fstream>

using namespace std;

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

int dq[5000000], v[5000000];
int st = 0, dr = -1;

int main()
{
	int n, k;
	long long s = 0;
	in >> n;
	in >> k;
	for (int i = 0; i < n; i++) {
		in >> v[i];
		if (st <= dr && dq[st] == i - k) {
			st++;
		}
		while (st <= dr && v[i] <= v[dq[dr]]) {
			dr--;
		}
		dq[++dr] = i;
		if (i >= k - 1) {
			s += v[dq[st]];
		}
	}
	out << s;
	return 0;
}