#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <iomanip>
#include <utility>
#include <tuple>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <deque>
#include <unordered_map>
#include <unordered_set>
#include <bitset>
#include <cctype>
#include <cassert>
#include <functional>
#include <numeric>
#include <type_traits>
using namespace std;
#define ll long long
#define rep(i, n) for (int i = 0; i < (n); i++)

int main() {
	int n, k;
	cin >> n >> k;
	vector<ll> a(n);
	rep(i, n) cin >> a[i];
	ll sum = 0, ans = 0;
	priority_queue<ll, vector<ll>, greater<ll>> q;
	for (int i = n - 1; i >= 0; i--) {
		if (i % 2) ans = max(ans, sum + a[i]);
		q.push(a[i]);
		sum += a[i];
		if (q.size() >= k) {
			sum -= q.top();
			q.pop();
		}
	}
	cout << ans << endl;
	return 0;
}