#include <bits/stdc++.h>
using namespace std;
const int nmax=1e5+5;
int dp[nmax],v[nmax];
int main()
{
    /*
    dp[i]=nr max de oua din primele i sectoare
    */
    ifstream fin ("oo.in");
    ofstream fout ("oo.out");
    int n;
    fin >> n;
    for (int i=1;i<=n;++i)
        fin >> v[i];
    dp[0]=dp[1]=dp[2]=0;
    for (int i=3;i<=n;++i)
        dp[i]=max(dp[i-1],dp[i-3]+v[i]+v[i-1]);
    int sol=dp[n-1];
    sol=max(sol,dp[n]);
    fout << sol;
    return 0;
}