#include <bits/stdc++.h>
using namespace std;
typedef long long int ll;
typedef pair<ll,ll> P;
typedef vector<ll> VI;
typedef vector<VI> VVI;
#define REP(i,n) for(ll i=0;i<(n);i++)
#define ALL(v) v.begin(),v.end()
template<typename T> bool chmax(T &x, const T &y) {return (x<y)?(x=y,true):false;};
template<typename T> bool chmin(T &x, const T &y) {return (x>y)?(x=y,true):false;};
constexpr ll MOD=998244353;
constexpr ll INF=2e18;

int main(){
    int n, k; cin >> n >> k;
    VI a(n); REP(i,n) cin >> a[i];
    priority_queue<ll,VI,greater<ll>> q;
    ll ans=0, s=0;
    for(int i=n-1;i>=0;i--){
        if(i%2==1)
            chmax(ans,s+a[i]);
        s+=a[i];
        q.push(a[i]);
        if(q.size()>=k){
            s-=q.top();
            q.pop();
        }
    }
    cout << ans << endl;
    return 0;
}