import java.util.Scanner;

class sushi2 {
	
	private static final int MAX_N = 1000;
	static int v[] = new int[MAX_N]; //sushiの価値
	
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		for (int i = 0; i < n; i++) {
			v[i] = sc.nextInt();
		}
		sc.close();
		int[] sum = {0,0};//{２個前までの合計,１個前までの合計}
		
		int b = 0;
		for (int i = 0 ; i < n ;i++) {
			b = Math.max(sum[0] + v[i] , sum[1]);
			sum[0] = sum[1];
			sum[1] = b;			
		}
		System.out.println(Math.max(sum[0], sum[1]));		
	}
}