#include <bits/stdc++.h>

using namespace std;

ifstream fin("oo.in");
ofstream fout("oo.out");

int n,dp[100005],i,v[100005],Max;

int main()
{
fin>>n;
for(i=1;i<=n;i++){
    fin>>v[i];
}
dp[2] = v[1] + v[2];
dp[3] = v[2] + v[3];
Max = max(Max,dp[2]);
Max = max(Max,dp[3]);
for(i=4;i<=n;i++){
    dp[i] = max(dp[i-3],dp[i-4]) + v[i] + v[i-1];
    Max = max(Max,dp[i]);
}
fout << Max;
    return 0;
}