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

const int NMAX = 5000000;

int n,k;
long long sum;
int a[NMAX];
deque<int> dq;

int main() {
	freopen("deque.in","rt",stdin);
	freopen("deque.out","wt",stdout);
	scanf("%d %d",&n,&k);
	sum = 0;
	for (int i = 0; i < n; ++i) {
		scanf("%d",&a[i]);
		while (!dq.empty() && dq.back() > a[i])
			dq.pop_back();
		dq.push_back(a[i]);
		if (i >= k && dq.front() == a[i-k]) dq.pop_front();
		if (i >= k-1) sum += (long long)dq.front();
	}
	printf("%lld\n",sum);
	return 0;
}