source_code: import java.util.*;
  import java.io.*;
  
  public class A {
  
      public static void main(String[] args) {
          Scanner s = new Scanner(new InputStreamReader(System.in));
          int n = s.nextInt();
          if (n == 1) {
              System.out.println("NO");
              System.exit(0);
          }
          int[] nums = new int[n];
          for (int i = 0; i < n; i++) {
              nums[i] = s.nextInt();
          }
          Arrays.sort(nums);
          int x = 1;
          while (x < n && nums[x] == nums[x - 1])
              x++;
          if (x == n) {
              System.out.println("NO");
              System.exit(0);
          } else {
              System.out.println(nums[x]);
              System.exit(0);
          }
  
      }
  }
  