import java.io.*;
import java.util.*;

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