#include <stdio.h>
#include <atcoder/all>
#include <bits/stdc++.h>
using namespace std;
using namespace atcoder;
using mint = modint998244353;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 1000000000

int main() {
    
	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>> Q;
	long long sum = 0;
	long long ans = 0;
	for(int i=N-1;i>=0;i--){
		if(i%2==1){
			ans = max(ans,a[i] + sum);
		}
		
		Q.push(a[i]);
		sum += a[i];
		if(Q.size()>K-1){
			sum -= Q.top();
			Q.pop();
		}
	}
	cout<<ans<<endl;
	
    return 0;
}