#include "iostream"
#include "climits"
#include "list"
#include "queue"
#include "stack"
#include "set"
#include "functional"
#include "algorithm"
#include "string"
#include "map"
#include "unordered_map"
#include "unordered_set"
#include "iomanip"
#include "cmath"
#include "random"
#include "bitset"
#include "cstdio"
#include "numeric"
#include "cassert"
#include "ctime"

using namespace std;

//constexpr long long int MOD = 1000000007;
constexpr long long int MOD = 998244353;
constexpr double EPS = 1e-8;

//int N, M, K, T, H, W, L, R;
long long int N, M, K, T, H, W, L, R;

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> N >> M;
	vector<int>v(N);
	for (auto& i : v)cin >> i;
	long long ans = 0;
	multiset<int>s;
	long long sum = 0;
	for (int i = N - 1; i > 0; i--) {
		if(i&1)ans = max(ans, sum + v[i]);
		s.insert(v[i]);
		sum += v[i];
		if (s.size() >= M) {
			sum -= *s.begin();
			s.erase(s.begin());
		}
	}
	cout << ans << endl;
}