import java.util.*;

public class Exercises20{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int numberOfSushi = sc.nextInt();

    int[] sushiArray = new int[numberOfSushi];

    for (int n = 0; n < numberOfSushi; n++){
      sushiArray[n] = sc.nextInt();
    }

    int[] dp = new int[2];
    for (int n = 0; n < numberOfSushi; n++){
      int[] dp2 = new int[2];
      dp2[0] = Math.max(dp[0], dp[1]);
      dp2[1] = dp[0] + sushiArray[n];
      dp = dp2;
    }

    System.out.println(Math.max(dp[0], dp[1]));
  }
}