#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define ALL(v) v.begin(),v.end()
typedef long long ll;

#include <bits/stdc++.h>
using namespace std;

int main(){
  ios::sync_with_stdio(false);
  std::cin.tie(nullptr);
  
  ll n,k;
  cin>>n>>k;
  vector<ll> A(n);
  rep(i,n) cin>>A[i];
  
  priority_queue<int,vector<int>,greater<int>> que;
  ll siz=0,sum=0,ans=0;
  for(int i=n-1;i>0;i--){
    if(i%2) ans=max(ans,sum+A[i]);
    if(siz<k-1){
      que.push(A[i]);
      sum+=A[i];
      siz++;
    }
    else if(siz>0){
      auto t=que.top();
      if(A[i]>t){
        que.pop();
        que.push(A[i]);
        sum+=A[i]-t;
      }
    }
  }
  cout<<ans<<endl;
  
  return 0;
}