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

class Main {
	
	public static void out (Object o) {
		System.out.println(o);
	}
	
	public static void main (String[] args) throws IOException {
		BufferedReader br = 
			new BufferedReader(new InputStreamReader(System.in));
		
		int n = Integer.parseInt(br.readLine());
		int[] v = new int[n];
		int[] d = new int[n];
		String[] s = br.readLine().split(" ");
		
		for (int i = 0; i < n; i++)
			v[i] = Integer.parseInt(s[i]);
		
		d[0] = v[0];
		d[1] = Math.max(v[0] , v[1]);
		for (int i = 2; i < n; i++)
			d[i] = Math.max(d[i - 1] , d[i - 2] + v[i]);
		
		out(d[n - 1]);
		
	}
}