#include<iostream>
#include<fstream>
using namespace std;
#define max 5000002
int main()
{
	ifstream f("deque.in");
	ofstream g("deque.out");
	int i, N, k, elem[max], deque[max], first = 1, last = 0;
	long long sum=0;

	f >> N >> k;
	
	for (i = 1; i <= N; i++) f >> elem[i];
	
	for (i = 1; i <= N; i++)
	{
		while (first <= last && elem[i] <= elem[deque[last]]) last--;
		deque[++last] = i;
		if (deque[first] + k == i) first++;
		if (i >= k) sum = sum + elem[deque[first]];
	}
	g << sum;
	return 0;
}