#include<bits/stdc++.h>
using namespace std;
#include <unordered_set>
#include <random>
//#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll inv2=499122177;
const ll MAX=200010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;

ll dx[]={0,1,0,-1,-1,-1,1,1};
ll dy[]={1,0,-1,0,-1,1,-1,1};


void solve(){
    ll n,k;cin>>n>>k;
    vector<ll>a(n);
    rep(i,n)cin>>a[i];
    priority_queue<ll,vector<ll>,greater<ll> >pq;
    ll sum=0;
    ll ans=0;
    for(int i=n-1;i>=0;i--){
        if(i%2){
            ans=max(ans,a[i]+sum);
        }
        sum+=a[i];
        pq.push(a[i]);
        if(pq.size()==k){
            ll s=pq.top();
            pq.pop();
            sum-=s;
        }
    }
    cout<<ans<<endl;
}

signed main(){
    cin.tie(0);
    ios::sync_with_stdio(false);
    solve();
}