#include <bits/stdc++.h>

using namespace std;
using ll = long long;
using ld = long double;

#define rep(i, r) for(int i = 0; i < (r); ++i)
#define reps(i, s, r) for(int i = (s); i < (r); ++i)
#define fore(i, m2) for(auto &i : m2)
#define vi vector<int>
#define vl vector<ll>
#define pl pair<ll, ll>
#define all(i) (i).begin(), (i).end()
#define fs first
#define sc second

template <class T> bool chmin(T &i, T b) {
    if(i > b) {
        i = b;
        return true;
    }
    return false;
}
template <class T> bool chmax(T &a, T b) {
    if(a < b) {
        a = b;
        return true;
    }
    return false;
}

const ll INF = LONG_LONG_MAX / 3;
const ll MOD = 1'000'000'007;
const ll MAX = 2e5 + 5;

int main() {

    ll n;
    cin >> n;
    vl a(n), dp(n + 3);
    rep(i, n) cin >> a[i];

    dp[0] = a[0];
    dp[1] = max(a[0], a[1]);

    reps(i, 2, n) {

        ll add = 0;
        if(i >= 2)
            dp[i] = max(dp[i - 1], dp[i - 2] + a[i]);
    }

    cout << dp[n - 1] << endl;
}