import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

public class No45 {

	public static void main(String[] args) throws IOException {
		
		String[] read = readStr();
		
		int N = Integer.parseInt(read[0]) , i = 0;
		String[] V = read[1].split(" ");
		
		int[] Vsum = new int[N];
		Vsum[0] = Integer.parseInt(V[0]);
		
		if(N > 1) {
			Vsum[1] = Math.max(Integer.parseInt(V[1]), Vsum[0]);
		}
		
		if(N > 2) {
			for(i = 2;i < N;i++) {
				Vsum[i] = Math.max(Vsum[i-2] + Integer.parseInt(V[i]), Vsum[i-1]);
			}
		}

		System.out.println(Vsum[N-1]);
		
	}
	
	public static String[] readStr() throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		ArrayList<String> list = new ArrayList<>();

		do {
			list.add(br.readLine());
		}while(br.ready());

		br.close();

		String[] text = new String[list.size()];
		list.toArray(text);

		return text;

	}

}