#include <iostream>
#include <fstream>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int deq[5000005],a[5000005];
long long sum;

int main()
{
	int n,k,head=1,tail=0;
    in>>n>>k;
    int i;
	for (i=1; i<=n; i++)
    {
        in>>a[i];
    }


	for (i=1; i<=n; i++)
	{

		while (head<=tail && a[i]<=a[deq[tail]])
            tail-=1;

		deq[++tail]=i;

		if (deq[head]==i-k)
            head+=1;

		if (i>=k)
            sum+=a[deq[head]];
	}

	out<<sum;

	return 0;
}