#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define pb push_back
#define mp make_pair
#define deb(x) cout<< #x << " " << x << "\n";
#define MAX 9223372036854775807
#define MIN -9223372036854775807
#define PI 3.141592653589
#define setbits(n) __builtin_popcountll(n)
#define mkunique(a) a.resize(unique(a.begin(),a.end())-a.begin());
const ll mod=1e9+7;


const int N=1e5+10;
ll dp[N][5],n;
vector<ll> a(N);

ll go(ll pos, ll s){
    if(pos==n){
        if(s<4) return -mod*mod;
        return 0;
    }
    if(dp[pos][s]!=-1)
        return dp[pos][s];
    ll ans;
    if(s==0)
        ans=max(go(pos+1,0),go(pos+1,1));
    else if(s==1)
        ans=max({a[pos]+go(pos+1,1),a[pos]+go(pos+1,2),a[pos]+go(pos+1,3)});
    else if(s==2)
        ans=max(go(pos+1,2),go(pos+1,3));
    else if(s==3)
        ans=max(a[pos]+go(pos+1,3),a[pos]+go(pos+1,4));
    else
        ans=go(pos+1,4);
    return dp[pos][s]=ans;
}

int main() {

    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    ll T=clock();

    cin>>n;
    for(ll i=0;i<n;i++)
        cin>>a[i];
    memset(dp,-1,sizeof(dp));
    cout<<max(go(0,0),go(0,1));


    cerr<<"\n\nTIME: "<<(double)(clock()-T)/CLOCKS_PER_SEC<<" sec\n";
    T = clock();
    return 0;
}