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

#ifdef _RUTHEN
#include "debug.hpp"
#else
#define show(...) true
#endif

using ll = long long;
#define rep(i, n) for (int i = 0; i < (n); i++)
template <class T> using V = vector<T>;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    ll N, K;
    cin >> N >> K;
    V<ll> A(N);
    rep(i, N) cin >> A[i];
    priority_queue<ll, vector<ll>, greater<ll>> que;
    ll cs = 0, ans = 0;
    for (int i = N - 1; i >= 0; i--) {
        if (i % 2 != 0) {
            // A[i] と K-1個
            while (que.size() > K - 1) {
                cs -= que.top();
                que.pop();
            }
            ans = max(ans, cs + A[i]);
        }
        que.push(A[i]);
        cs += A[i];
    }
    cout << ans << '\n';
    return 0;
}