#include <bits/stdc++.h>
using namespace std;
typedef  long long int ll;



int main() {
    cin.tie(0);
    ios::sync_with_stdio(false);
    int n;
    cin >> n;
    int a[n+10], dp[n+10];
    
    
    for (int i = 1; i <= n; i++)
        cin >> a[i];
    
    dp[1] = a[1];
    dp[2] = max(a[1], a[2]);
    
    for (int i = 3; i <= n; i++) {
        dp[i] = max(dp[i-1], dp[i-2] + a[i]);
    }
    cout << dp[n] << endl;



    return 0;
}