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

const string file = "oo";
ifstream fin(file+".in");
ofstream fout(file+".out");

const int dim = 100001;
int n, i, a[dim], dp[dim], mxdp[dim];

int main()
{
    fin >> n;
    for (i = 1; i <= n; i++)
        fin >> a[i];
    int rez = 0;
    dp[0] = dp[1] = mxdp[0] = mxdp[1] = 0;
    dp[2] = mxdp[2] = a[1]+a[2];
    for (i = 3; i <= n-1; i++)
    {
        dp[i] = a[i-1]+a[i]+mxdp[i-3];
        mxdp[i] = max(dp[i], mxdp[i-1]);
    }
    rez = mxdp[n-1];
    dp[0] = dp[1] = mxdp[0] = mxdp[1] = dp[2] = mxdp[2] = 0;
    for (i = 3; i <= n; i++)
    {
        dp[i] = a[i-1]+a[i]+mxdp[i-3];
        mxdp[i] = max(dp[i], mxdp[i-1]);
    }
    rez = max(rez, mxdp[n]);
    fout << rez;
    return 0;
}