import java.util.Scanner;
class Main{
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int[] data = new int [sc.nextInt()];
		int[] vect = new int [data.length];
		
		for(int i = 0 ; i < data.length ; i++)data[i] = sc.nextInt();
		if(data.length == 1) {
			System.out.println(data[0]);
			return;
		}
		if(data.length == 2) {
			if(data[0] < data[1])System.out.println(data[1]);
			else System.out.println(data[0]);
			return;
		}
		vect[0] = data[0];
		vect[1] = data[1];
		for(int i = 2 ; i < data.length ; i++) {
			int max = 0;
			for(int j = 0 ; j < i - 1 ; j++) {
				if(data[i] + vect[j] > max)max = data[i] + vect[j];
			}
			vect[i] = max;
		}
		int max = 0;
		for(int i = 0 ; i < vect.length ; i++) 
			if(max < vect[i])max = vect[i];
		System.out.println(max);
	}
}