#include <cstdio>
#include <set>

using namespace std;

int n, k;
int A[5000000];

int main() {
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	scanf("%d%d", &n, &k);
	for (int i = 0; i < n; i++) {
		scanf("%d", A + i);
	}
	multiset<int> data;
	for (int i = 0; i < k; i++) {
		data.insert(A[i]);
	}
	long long ans = *data.begin();
	for (int i = k; i < n; i++) {
		data.erase(data.find(A[i - k]));
		data.insert(A[i]);
		ans += *data.begin();
	}
	printf("%lld", ans);
	return 0;
}