#include <fstream>
#define maxn 5000001
using namespace std;
int n, k,i;
int A[maxn], coada[maxn];
int Front=1, Back;
long long Sum;

int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	f>>n>>k;
	for (i = 1; i <= n; i++) f>>A[i];
	for (i = 1; i <= n; i++)
	{
		while (Front <= Back && A[i] <= A[ coada[Back] ]) Back--;		
		coada[++Back] = i;
		if (coada[Front] == i-k) Front++;
		if (i >= k) Sum += A[coada[Front]]; 	
	}
	g<<Sum;
    g.close(); 
	return 0;
}