#include <bits/stdc++.h>
#include <fstream>

int N, K;
int v[5000001], deq[5000001];
int F,B;
unsigned long long S;
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int main()
{

	int i;

	f>>N>>K;

	for (i = 1; i <= N; i++)
		f>>v[i];

	F=1, B=0; //

	for (i = 1; i <= N; i++)
	{

		while (F <= B  && v[i] <= v[deq[B]])
            B--;

		deq[++B] = i;

		if (deq[F] == i-K)
            F++;


		if (i >= K)
            S+= v[deq[F]];
	}

	g<<S;

	return 0;


}