#include <iostream>
#include <algorithm>
using namespace std;

int ssh(int *d, int n)
{
    if(n < 0) return 0;
    return max(ssh(d, n-2) + d[n], ssh(d, n-1));
}

int main()
{
    int n, v[1000] = {0};
    cin >> n;
    for(int i = 0; i < n; i++){
        scanf("%d", &v[i]);
    }
    cout << ssh(v, n-1) << endl;
    return 0;
}