import java.util.*;
 

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int[] susi=new int[n];
		int[] dp = new int[n];
		for(int i=0;i<n;i++){
			susi[i]=sc.nextInt();
		}
		dp[0]=susi[0];
		if(n==1){
			System.out.println(dp[0]);
			return;
		}
		dp[1]=Math.max(susi[0],susi[1]);
		if(n==2){
			System.out.println(dp[1]);
			return;
		}
		for(int i=2;i<n;i++){
			dp[i]=Math.max(dp[i-1],dp[i-2]+susi[i]);
		}
		System.out.println(dp[n-1]);
	}
}