import java.util.Scanner;

import static java.lang.Math.*;

public class Main {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt(), s = 0;

        for (int i = 0; i < n; i++)
        {
            int r = sc.nextInt();
            if (r < 0)
                s = 1;
        };

        System.out.println(s == 1 ? "YES" : "NO");
    }
}