source_code: /*
   * To change this template, choose Tools | Templates
   * and open the template in the editor.
   */
  //package a_vtoray_poriadkovay_statistika;
  
  import java.util.Arrays;
  import java.util.Scanner;
  
  /**
   *
   * @author kal1sha
   */
  public class Main {
  
      /**
       * @param args the command line arguments
       */
      public static void main(String[] args) {
          // TODO code application logic hereSc
          int n, i;
          boolean status = false;
          int answer;
          Scanner in = new Scanner(System.in);
          n = in.nextInt();
          int a[] = new int[n];
          for (i = 0; i < n; i++) {
              a[i] = in.nextInt();
          }
          Arrays.sort(a);
          answer = a[0];
          for (i = 1; i < n; i++) {
              if (a[i] != answer) {
                  answer = a[i];
                  status = true;
                  i = n + 1;
              }
          }
          if (status) {
              System.out.println(answer);
          } else {
              System.out.println("NO");
          }
      }
  }
  