#include <stdio.h>
#include <iostream>
#include <vector>
#include <queue>
#include <stack>
#include <algorithm>

#pragma GCC optimize("O2")

using ll = long long int;
using P = std::pair<ll, int>;
const int INF = (1<<30);
const ll INFLL = (1ll<<60);
const ll MOD = (ll)(1e9+7);

#define l_ength size

void mul_mod(ll& a, ll b){
	a *= b;
	a %= MOD;
}

void add_mod(ll& a, ll b){
	a = (a<MOD)?a:(a-MOD);
	b = (b<MOD)?b:(b-MOD);
	a += b;
	a = (a<MOD)?a:(a-MOD);
}

ll a[225816],s[225816],dp[225816][2];
std::priority_queue<P> pq;

int main(void){
	int n,m,i;
	ll ans = -INFLL;
	std::fill(dp[0],dp[225816],-INFLL);
	std::cin >> n >> m; --m;
	dp[0][0] = 0ll;
	pq.push(P(0ll,0));
	for(i=0; i<n; ++i){
		std::cin >> a[i];
		s[i+1] = s[i] + a[i];
	}
	for(i=1; i<=n; ++i){
		while(pq.top().second < i-m){
			pq.pop();
		}
		dp[i][1] = pq.top().first + s[i];
		dp[i][0] = std::max(dp[i-1][0],dp[i-1][1]);
		pq.push(P(dp[i][0]-s[i],i));
	}
	for(i=0; i<=n; ++i){
		ans = std::max(ans,std::max(dp[i][0],dp[i][1]));
	}
	std::cout << ans << std::endl;
	return 0;
}