import java.util.*;
public class Main {

  public static void main(String[] args) { 
      Scanner sc = new Scanner(System.in);
      int n = sc.nextInt();
      int prevPrev = sc.nextInt();
      if(n == 1) {
          System.out.println(prevPrev);
          return;
      }
      
      int prev = Math.max(prevPrev, sc.nextInt());
      int res = Math.max(prevPrev, prev);
      for(int i = 3; i <= n; i++) {
        int num = sc.nextInt();
        res = Math.max(num + prevPrev, prev);
        prevPrev = prev;
        prev = res;
      }
      System.out.println(res);
  }
}