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

LyogcGFja2FnZSB3aGF0ZXZlcjsgLy8gZG9uJ3QgcGxhY2UgcGFja2FnZSBuYW1lISAqLwoKaW1wb3J0IGphdmEudXRpbC4qOwppbXBvcnQgamF2YS5sYW5nLio7CmltcG9ydCBqYXZhLmlvLio7CgovKiBOYW1lIG9mIHRoZSBjbGFzcyBoYXMgdG8gYmUgIk1haW4iIG9ubHkgaWYgdGhlIGNsYXNzIGlzIHB1YmxpYy4gKi8KY2xhc3MgSWRlb25lCnsKCXB1YmxpYyBzdGF0aWMgdm9pZCBtYWluIChTdHJpbmdbXSBhcmdzKSB0aHJvd3MgamF2YS5sYW5nLkV4Y2VwdGlvbgoJewoJCS8vIHlvdXIgY29kZSBnb2VzIGhlcmUKCQlTY2FubmVyIHNjPW5ldyBTY2FubmVyKFN5c3RlbS5pbik7CgkJaW50IG49c2MubmV4dEludCgpOwoJCQoJCWludCBhW109bmV3IGludFtuKzFdOwoJCWZvcihpbnQgaT0xO2k8PW47aSsrKQoJCWFbaV09c2MubmV4dEludCgpOwoJCQoJCWludCBkcFtdPW5ldyBpbnRbbisxXTsKCQkKCQlkcFsxXT1hWzFdOwoJCWRwWzJdPU1hdGgubWF4KGRwWzFdLGFbMl0pOwoJCQoJCWZvcihpbnQgaT0zO2k8PW47aSsrKQoJCWRwW2ldPU1hdGgubWF4KGRwW2ktMV0sYVtpXStkcFtpLTJdKTsKCQkKCQlTeXN0ZW0ub3V0LnByaW50bG4oZHBbbl0pOwoJCQoJfQp9

NQoyIDQgNiA3IDg=

5
2 4 6 7 8