#include<fstream>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int v[5000001], deque[5000001];
int front, back,n,k,i;
long long sum;

int main()
{	fin >> n >> k;
	for (i=1;i<=n;i++) 
		fin >> v[i];
	for (i=1;i<=n;i++)
	{	while (front <= back && v[i] <= v[deque[back] ]) 
			back--;		
		deque[++back] = i;
		if (deque[front] == i-k) 
			front++;
		if (i >= k) 
			sum += v[deque[front]]; 	
	}
	fout << sum;
	return 0;
}