#include <cstdio>
#include <deque>
#define dim 5000100

using namespace std;

int n, k, sum=0, d[dim];
deque<int> q;

int main()
{
	int i;
	freopen("deque.in", "r", stdin);
	freopen("deque.out", "w", stdout);
	scanf("%d %d\n", &n, &k);
	for (i=1; i<=n; i++) scanf("%d\n", &d[i]);
	for (i=1; i<=k; i++)
	{
		while (!q.empty() && d[i]<d[q.back()])
			q.pop_back();
		q.push_back(i);
	}
	sum+=d[q.front()];
	for (i=k+1; i<=n; i++)
	{
		while (!q.empty() && d[i]<d[q.back()])
			q.pop_back();
		q.push_back(i);
		while (!q.empty() && q.front()<=i-k) q.pop_front();
		sum+=d[q.front()];
	}
	printf("%d\n", sum);
}