#include <fstream>
using namespace std;

ifstream cin("oo.in");
ofstream cout("oo.out");

#define int long long

int v[100002];

int solve(int a,int b){
    int dp[100002],i;
    dp[a]=0;
    dp[a+1]=v[a]+v[a+1];
    for(i=a+2;i<=b;i++)
        dp[i]=max(dp[i-1],dp[i-3]+v[i-1]+v[i]);
    return dp[b];
}

signed main()
{
    int n,i;
    cin>>n;
    for(i=1;i<=n;i++)
        cin>>v[i];
    v[0]=v[n];v[1]=v[n+1];
    cout<<max(solve(1,n-1),max(solve(2,n),solve(3,n+1)));
    return 0;
}