import java.util.*;
import java.lang.*;
import java.io.*;
 
class Ideone
{
    public static void main (String[] args) throws java.lang.Exception
    {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt(); // array size
        int[] a = new int[n];
        for (int i = 0; i < n; i++) a[i] = sc.nextInt();
 
        if (n == 0) {
            System.out.println(0);
            return;
        }
 
        if (n == 1) {
            System.out.println(a[0]);
            return;
        }
 
        int[] dp = new int[n];
        dp[0] = a[0];
        dp[1] = Math.max(a[0], a[1]);
 
        for (int i = 2; i < n; i++) {
            dp[i] = Math.max(dp[i - 1], dp[i - 2] + a[i]);
        }
 
        System.out.println(dp[n - 1]);
    }
}
 

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