import java.util.*;

public class Exercises19{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int numberOfSushi = sc.nextInt();

    int[] sushiArray = new int[numberOfSushi];

    ArrayDeque<Sushi> stack = new ArrayDeque<Sushi>();
    int sum = 0;

    for (int n = 0; n < numberOfSushi; n++){
      sushiArray[n] = sc.nextInt();
      stack.add(new Sushi(sushiArray[n], n));
    }

    while (stack.size() > 0){
      Sushi sushi = stack.pop();

      if(sushi.indexOfSushi + 1 >= numberOfSushi - 1){
        if (sum < sushi.sumOfTaste) {
          sum = sushi.sumOfTaste;
        }
      }else{
        int maxTaste = 0;
        for (int n = (sushi.indexOfSushi + 2); n < numberOfSushi; n++){
          if (maxTaste < sushiArray[n]){
            maxTaste = sushiArray[n];
            stack.push(new Sushi(sushi.sumOfTaste + sushiArray[n], n));
          }
        }
      }
    }
    System.out.println(sum);
  }
}

class Sushi {
  public int sumOfTaste;
  public int indexOfSushi;

  Sushi(int sum, int index){
    sumOfTaste = sum;
    indexOfSushi = index;
  }
}