#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, k; cin >> n >> k;
	vector<long long>a(n);
	rep(i, n)cin >> a[i];
	priority_queue<long long, vector<long long>, greater<long long>>pq;
	long long sum = 0;
	long long ans = 0;
	rrep(i, n) {
		if ((1 == i % 2) && ((k - 1) == pq.size())) {
			chmax(ans, a[i] + sum);
		}
		if ((k - 1) != pq.size()) {
			pq.push(a[i]);
			sum += a[i];
		}
		else {
			if ((1 != k) && (a[i] > pq.top())) {
				sum -= pq.top();
				sum += a[i];
				pq.pop();
				pq.push(a[i]);
			}
		}
	}
	cout << ans << endl;
	return 0;
}