//#include "stdafx.h"
#include <iostream>
#include <fstream>
#include <deque>
#include <utility>

using namespace std;

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

long long N, x, K, suma=0;

//n = nr de numere din sir
//k = secventa de numere
//x = numarul citit

deque < pair<long long, long long> > deq;

int main()
{
	f >> N >> K;
	for ( long long i=0; i<N; ++i )
	{
		f >> x;
		while ( !deq.empty() && deq.back().first >= x )
			deq.pop_back();

		deq.push_back( make_pair(x, i) );

		if ( deq.front().second <= i-K )
			deq.pop_front();

		if (i >= K-1)
			suma += deq.front().first;
	}
	g << suma;
}