import java.util.*;

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