/* 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
	{
		// your code goes here
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int a[] = new int[n];
		for(int i=0; i<n ; i++){
			a[i] = sc.nextInt();
		}
 
		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-2]+a[i], dp[i-1]);
		}
 
		System.out.println(dp[n-1]);
 
	}
}

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NgoyIDQgNSA4IDEwIDEy

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