#include <bits/stdc++.h>
const int NMAX = 1e5;
using namespace std;
int v[NMAX + 5], n;
int solve(int start, int endd){
    int dp[NMAX + 5] = {0};
    dp[start + 1] = v[start] + v[start + 1];
    for (int i = start + 2; i <= endd; ++i)
        dp[i] = max(dp[i - 1], dp[i - 3] + v[i - 1] + v[i]);
    return dp[endd];
}
signed main(){
    cin >> n;
    for (int i = 1; i <= n; ++i)
        cin >> v[i];
    cout << max({solve(1, n - 1), solve(2, n), solve(3, n  + 1)});
    return 0;
}