import java.util.Scanner;

public class No45 {
	public static void main(String[] args) {
		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];
		if(N >= 2) {
			dp[1] = Math.max(dp[0],V[1]);
		}
		
		for(int i = 2;i < N;i++) {
			dp[i] = Math.max(dp[i-1],dp[i-2]+V[i]);
		}
		
		System.out.println(dp[N-1]);
	}
}