package yukicoder045;
import java.util.Scanner;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		
		int n=sc.nextInt();
		int[] v=new int[n];
		int[] dp=new int[n];
		for(int i=0;i<n;i++){
			v[i]=sc.nextInt();
		}
		dp[0]=v[0];
		if(n>1)dp[1]=Math.max(v[0],v[1]);
		for(int i=2;i<n;i++){
			dp[i]=Math.max(dp[i-1],dp[i-2]+v[i]);
		}
		System.out.println(dp[n-1]);
	}
}