#include<bits/stdc++.h>
using namespace std;
typedef pair<int, int> pii;
typedef long long int ll;

int n, ans;
int a[1001];

void f(int pos, int p, int sum) {
    //cout << pos << " : " << p << " : " << sum << endl;
    if (pos > n) {
        if (sum > ans)
            ans = sum;
        return;
    }
    
    f(pos+2, p+1, sum+a[pos]);
    f(pos+1, p, sum);
    
}

int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
 
    cin >> n;
    for (int i = 0; i < n; i++)
        cin >> a[i];
    
    f(0, 0, 0);
    cout << ans << endl;
  
    return 0;
}