#include <iostream>
#include <fstream>

using namespace std;
#define maxn 5000010

int n, k, i, p, u, s;
int a[maxn], Deque[maxn];

int main()
{
	ifstream in("deque.in");
	ofstream out("deque.out");

	in>>n>>k;

	for(i = 1; i <= n; i++)
		in>>a[i];

	p = 1;
	u = 0;

	for(i = 1; i <= n; i++)
	{
		while(p <= u && a[i] <= a[ Deque[u] ]) u--;
		Deque[++u] = i;
		if(Deque[p] == i-k) p++;
		if (i >= k) s += a[ Deque[p]];
	}

	out<<s;

	return 0;
}