#include <iostream>
#include <fstream>
using namespace std;
int main()
{
	int n, k, v[5000010], deq[5000010], i, st=1, dr=0, suma=0;
	ifstream f("deque.in");
	f >> n >> k;
	for (i = 0; i < n; i++)
		f >> v[i];
	f.close();	
	for (i = 1; i < n; i++)
	{
		while (st <= dr && v[i] < v[deq[dr]])
			dr--;
		deq[++dr] = i;
		if (deq[st] == i - k)
			st--;
		if (i >= k)
			suma += v[deq[st]];
	}
	ofstream g("deque.out");
	g << suma;
}