#include <iostream>
#include <fstream>
#include <deque>

using namespace std;

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

const int nmax = 5005000;
int n, v[nmax], k;
deque < pair <int, int> > D;
long long Suma;

void rezolvare(){
	deque < pair <int, int> > :: iterator it;

	for(int i = 1; i <= k; ++i){

		while( !D.empty() && v[i] <= D[ D.size() - 1].first )
			D.pop_back();

		D.push_back( make_pair(v[i], i) );
	}

	Suma += D[0].first;

	if(D[0].second == 1)
		D.pop_front();

	for(int i = k + 1; i <= n; ++i){

		it = D.end();
		while( !D.empty() && v[i] <= D[ D.size() - 1].first  )
			D.pop_back();

		D.push_back( make_pair(v[i], i) );

		Suma += D[0].first;
		
		if( D[0].second == i - k + 1)
			D.pop_front();
	}
}

int main(){
	f>>n>>k;

	for(int i = 1; i <= n; ++i)
		f>>v[i];
	rezolvare();

	g<<Suma<<'\n';

	return 0;
}