#include <cstdio>
#include <deque>
using namespace std;


int i, n, k;
int v[5000007] = { 0 };
long long sum = 0;
deque <int> q;

int main() {

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

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

	for (i = 1; i <= n; i++) {
		scanf("%d", &v[i]);
		while (!q.empty() && v[q.back()] > v[i]) {
			q.pop_back();
		}
		q.push_back(i);
		if (q.front() == i - k) q.pop_front();
		if (i >= k && !q.empty()) sum += (long long)v[q.front()];

	}
	
	printf("%lld", sum);

	return 0;
}