#define ll long long
#include <bits/stdc++.h>
using namespace std;
int main()
{
ios::sync_with_stdio(false);
cin.tie(0);
ll n;
cin>>n;
vector<ll> a(n);
for(ll& i : a)
cin>>i;
vector<ll> pre = {0}; //Greater than everything after that (index)
vector<ll> dp(n, 0); //Greatest usable pair of a, b if dp[i] is c
for(ll j = 1; j < n; j++)
{
ll p = pre.size();
for(ll i = 0; i < p; i++)
{
ll ind = pre[p-i-1];
ll minc = 2*(j+1) - (ind+1);
if(minc > n)
continue;
dp[minc-1] = max(dp[minc-1], a[j]+a[ind]);
if(a[ind] >= a[j])
break;
}
while(pre.size() && a[pre.back()] <= a[j])
pre.pop_back();
pre.push_back(j);
}
ll output = 0;
for(ll i = 1; i < n; i++)
{
dp[i] = max(dp[i], dp[i-1]);
output = max(output, dp[i]+a[i]);
}
cout<<output<<"\n";
}
