#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;
typedef unsigned long long ull;
//using mint = modint1000000007;
//using mint = modint998244353;



int main(){
  int N, K;
  cin >> N >> K;
  vector<ll> v(N);
  rep(i,N) cin >> v[i];

  ll ret = 0;
  ll sum = 0;
  priority_queue<ll,vector<ll>,greater<ll>> que;
  for(int i=N-1; i>=0; i--){
    if(i%2 == 1){
      ret = max(ret, v[i] + sum);
    }
    sum += v[i];
    que.push(v[i]);
    if(que.size() >= K){
      sum -= que.top();
      que.pop();
    }
  }
  
  cout << ret << endl;
  
  return 0;
}