#include <bits/stdc++.h>
using namespace std;
#include <atcoder/all>
using namespace atcoder;
using ll = long long;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using VS = vector<string>;
using VVS = vector<VS>;
using P = pair<ll,ll>;
using VP = vector<P>;
#define rep(i, n) for (ll i = 0; i < ll(n); i++)
#define out(x) cout << x << endl
#define dout(x) cout << fixed << setprecision(10) << x << endl;
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()
#define sz(x) (int)(x.size())
#define re0 return 0
#define pcnt __builtin_popcount
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
//const int INF = 1001001001;
const ll INF = 1e18;
//using mint = modint1000000007;
//using mint = modint998244353;
int di[8] = {0,0,-1,1,1,1,-1,-1};
int dj[8] = {1,-1,0,0,1,-1,1,-1};

int main(){
    ll n,k;
    cin >> n >> k;
    VL a(n);
    rep(i,n) cin >> a[i];
    ll ans = 0;
    ll sum = 0;
    multiset<ll> st;
    for(ll i = n-1;i > n-k;i--){
        sum += a[i];
        st.insert(a[i]);
    }
    for(ll i = n-k;i >= 0;i--){
        if(i%2 == 1){
            chmax(ans,a[i]+sum);
        }
        if(sz(st) == 0) continue;
        int mn = *st.begin();
        if(mn < a[i]){
            sum -= mn;
            sum += a[i];
            st.erase(st.find(mn));
            st.insert(a[i]);
        }
    }
    out(ans);
}