/* 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 dp[]=new int[n+1];
		int a[]=new int[n+1];
		for(int i=1;i<=n;i++)
		a[i]=sc.nextInt();
 
		dp[1]=a[1];
		dp[2]=dp[1]+a[2];
		dp[3]=Math.max(dp[2],dp[1])+a[3];
 
		for(int i=4;i<=n;i++)
		dp[i]=Math.max(Math.max(dp[i-1],dp[i-2]),dp[i-3])+a[i];
 
		System.out.println(dp[n]);
	}
}

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NQoyIDMgNCA1IDY=

5
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