#include <bits/stdc++.h>
#include <climits>
using namespace std;

int main(){
    int n;
    cin >> n;

    vector<int> vs(n + 3, 0);
    for (auto i = 1; i <= n; ++i) {
        cin >> vs[i];
    }

    vector<int> dp(n + 3, 0);

    dp[0] = 0;
    dp[1] = vs[1];
    for (auto i = 2; i <= n; ++i) {
        dp[i] = max(dp[i - 2] + vs[i], dp[i - 1]);
    }

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