#include <cstdio>
#include <deque>

const int NMAX = 5000005;
int n, k, a[NMAX];
long long result;

int main() {
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);

	scanf("%d %d", &n, &k);

	for (int i = 1; i <= n; i++) {
		scanf("%d", &a[i]);
	}

	std::deque<int> d;
	for (int i = 1; i < k; i++)
		d.push_back(a[i]);

	for (int i = k; i <= n; i++) {
		while (d.size() > k - 1)
			d.pop_front();

		while (!d.empty() && d.front() > a[i])
			d.pop_front();

		d.push_back(a[i]);

		result += d.front();
	}


	printf("%lld", result);

	return 0;
}