source_code: import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Scanner;
  
  
  public class CF22_1 {
  
      public static void main(String[] args) {
          Scanner sc=new Scanner(System.in);
          int num=sc.nextInt();
      if(num!=1)
      {
          ArrayList<Integer>data=new ArrayList<Integer>();
          for (int i=0;i<num;i++){
              data.add(sc.nextInt());
              
          }
          Collections.sort(data);
          
          int ind=1;
      
          while( data.get(ind-1)==data.get(ind) )
              {
              ind++;
              if(ind ==data.size())
                  break;
              }
          
          if(data.size()>ind)
          System.out.println(data.get(ind));
          else
              System.out.println("NO");
          
          
      }
      else
          System.out.println("NO");
      }
      
  }
  