#include<bits/stdc++.h>
#include<time.h>
using namespace std;

using ll = long long;
#define rep(i,n) for(ll i=0;i<ll(n);i++)
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vvvvll = vector<vvvll>;
using vb = vector<bool>;
using vvb = vector<vb>;
using vvvb = vector<vvb>;
using vvvvb = vector<vvvb>;

bool DEB = 0;

bool isbool(ll N){
    if(N<=1)return 0;
    for(ll i=2;i*i<=N;i++){
        if(N%i==0)return 0;
    }
    return 1;
}

ll modPow(ll a,ll n,ll mod){
    a%=mod;
    if(n==0)return 1;
    if(n%2==1)return (modPow(a,n-1,mod)*a)%mod;
    ll res=modPow(a,n/2,mod);
    return (res*res)%mod;
}
int main() {

    ll N,K;
    cin>>N>>K;
    multiset<ll> S;
    ll sum=0;
    vll A(N);
    ll an=0;
    rep(i,N)cin>>A[i];
    rep(i,K-1){
        S.insert(A[N-1-i]);
        sum+=A[N-1-i];
    }
    for(ll i=N-K;i>=0;i--){
        if(i%2==1){
            an=max(an,sum+A[i]);
        }
        sum+=A[i];
        S.insert(A[i]);
        auto p=S.begin();
        sum-=*p;
        S.erase(p);
    }
    cout<<an<<endl;
}