#include <bits/stdc++.h>
using namespace std;
 
typedef long long ll;
typedef pair<int,int> P;
 
const int INF = 1e9;
const int mod = 1e9+7;
const double EPS = 1e-10;
const double PI = acos(-1.0);

int dp[1010];

int main()
{
    int n;
    cin >> n;
    vector<int> v(n+10,0);
    for(int i = 0; i < n; i++) cin >> v[i];
    dp[0] = v[0];
    dp[1] = v[1];
    for(int i = 0; i < n; i++){
        dp[i+2] = max(dp[i]+v[i+2],dp[i+2]);
        dp[i+3] = max(dp[i]+v[i+3],dp[i+3]);
    }
    cout << dp[n-1] << endl;
    return 0;
}