#include <vector>
#include <string> 
#include <set> 
#include <map> 
#include <queue> 
#include <bitset> 
#include <stack>
#include <list>

#include <numeric> 
#include <algorithm> 

#include <cstdio>
#include <fstream>
#include <iostream> 
#include <sstream> 
#include <iomanip>

#include <cctype>
#include <cmath> 
#include <ctime>
#include <cassert>

using namespace std;

#define LL long long
#define PII pair <int, int>
#define VB vector <bool>
#define VI vector <int>
#define VD vector <double>
#define VS vector <string>
#define VPII vector <pair <int, int> >
#define VVI vector < VI >
#define VVB vector < VB >

#define FORN(i, n) for(int i = 0; i < (n); ++i)
#define FOR(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)
#define FORI(it, X) for(__typeof((X).begin()) it = (X).begin(); it !=(X).end(); ++it) 
#define REPEAT do{ 
#define UNTIL(x) }while(!(x)); 

#define SZ size()
#define BG begin() 
#define EN end() 
#define CL clear()
#define X first
#define Y second
#define RS resize
#define PB push_back
#define MP make_pair
#define ALL(x) x.begin(), x.end()

#define IN_FILE "deque.in"
#define OUT_FILE "deque.out"

ifstream fin(IN_FILE);
ofstream fout(OUT_FILE);

int n, k;
VI a;
deque<PII> deq;

void add(int ind)
{
	while (!deq.empty() && deq.back().X > a[ind])
	{
		deq.pop_back();
	}
	deq.push_back(MP(a[ind], ind));
}


int main()
{
	fin >> n >> k;
	a.RS(n + 1);
	FOR(i, 1, n) fin >> a[i];
	fin.close();

	
	FOR(i, 1, k) add(i);

	LL sol = deq.front().X;
	FOR(i, 1, n - k)
	{
		while (!deq.empty() && deq.front().Y <= i)
		{
			deq.pop_front();
		}
		add(i + k);
		sol += deq.front().X;
	}

	fout << sol;
	fout.close();

	return 0;
}