#include <iostream>
#include <algorithm>
using namespace std;
int memo[1000][2] = {0};

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

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;
}