/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int n;
		Scanner in = new Scanner(System.in);
		n = in.nextInt();
		int[] dp = new int [n+1];
		for(int i = 1; i<=n; ++i){
        		dp[i] = in.nextInt();
		}
		dp[0] = 0;
		dp[1] = 0;
		for(int i = 2; i<=n; ++i){
    		if(i - 3 >= 0)
        		dp[i] = dp[i] + Math.max(dp[i-2], dp[i-3]);
		}
		System.out.print(dp[n]);
	}
}

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