source_code: import java.util.*;
  import java.io.*;
  public class Main{
  
          BufferedReader in;
          StringTokenizer str = null;
          PrintWriter out;
  
          private String next() throws Exception{
                  if (str == null || !str.hasMoreTokens())
                          str = new StringTokenizer(in.readLine());
                  return str.nextToken();
          }
          
          private int nextInt() throws Exception{
                  return Integer.parseInt(next());
          }
          
          private long nextLong() throws Exception{
                  return Long.parseLong(next());
          }
          
          private double nextDouble() throws Exception{
                  return Double.parseDouble(next());
          }
  
          public void run() throws Exception{
                  in = new BufferedReader(new InputStreamReader(System.in));//new FileReader();
                  out = new PrintWriter(System.out);//new File();
                  int n = nextInt();
                  HashSet<Integer> hs = new HashSet<Integer>();
                  for(int i=0;i<n;i++) hs.add(nextInt());
                  if (hs.size() == 1){
                    out.println("NO");
                    out.close();
                    return;
                  }
                  int a[] = new int[hs.size()];
                  int yk = 0;
                  for(int i:hs) a[yk++] = i;
                  Arrays.sort(a);
                  out.println(a[1]);
                  out.close();
          }
  
          public static void main(String args[]) throws Exception{
                  new Main().run();
          }
  }
   
  