typedef long long ll;
typedef long double ld;
#include <bits/stdc++.h>
using namespace std;
#define int long long
signed main(){
    ll n,k;
    std::cin >> n>>k;
    vector<ll> a(n);
    ll tsum = 0;
    typedef pair<ll,ll> pll;
    priority_queue<pll> pq;
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
        tsum += a[i];
        if(i>1){
            pq.push({a[i],i});
        }
    }
    ll sum = 0;
    vector<bool> used(n);
    for (int i = 0; i < k-1; i++) {
        auto [ai,ind] = pq.top();pq.pop();
        sum += ai;
        used[ind]=true;
    }
    ll ans = 0;
    for (int i = 0; i < n/2&&2*i+1<n-(k-1); i++) {
        for (int j = 2*i; j < 2*i+2; j++) {
            if(used[j]){
                sum -= a[j];
                while(true){
                    auto [ai,ind] = pq.top();pq.pop();
                    if(ind<=2*i+1)continue;
                    used[ind]=true;
                    sum += ai;
                    break;
                }
            }
        }
        ans = max(ans, a[2*i+1]+sum);
    }
    std::cout << ans << std::endl;
}