#include <fstream>

 using namespace std;
 ifstream f("deque.in");
 ofstream g("deque.out");


int n,k;
int a[5000010], Deque[5000010];
int fr,bk,i;
long long s;

int main()
{




	f>>n>>k;

	for (i = 1; i <= n; i++)
	f>>a[i];
fr = 1, bk = 0;
	for (i = 1; i <= n; i++)
	{while (fr <= bk && a[i] <=a[ Deque[bk] ])
	    bk--;
		Deque[++bk] = i;
		if (Deque[fr] == i-k) fr++;
		if (i >= k)
        s=s+a[Deque[fr]];
	}

g<<s;

	return 0;
}