source_code: import java.io.BufferedReader;
  import java.io.BufferedWriter;
  import java.io.IOException;
  import java.io.InputStreamReader;
  import java.io.OutputStreamWriter;
  import java.io.PrintWriter;
  import java.util.Collections;
  import java.util.LinkedList;
  import java.util.List;
  import java.util.Set;
  import java.util.StringTokenizer;
  import java.util.TreeSet;
  
  
  public class order {
  	public static void main(String[] args) throws IOException {
  		BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
  		PrintWriter out = new PrintWriter(new BufferedWriter(
  				new OutputStreamWriter(System.out)));
  		int n=Integer.parseInt(in.readLine());
  		Set<Integer> set = new TreeSet<Integer>();
  		StringTokenizer st= new StringTokenizer(in.readLine());
  		int a;
  		List<Integer> list =new LinkedList<Integer>();
  		while(st.hasMoreTokens()){
  			a= Integer.parseInt(st.nextToken());
  			if(!set.contains(a)){
  				list.add(a);
  				set.add(a);
  			}
  			
  		}
  		if(list.size()==1){
  			out.println("NO");
  		}else{
  			Collections.sort(list);
  			out.println(list.get(1));
  		}
  		out.close();
  		System.exit(0);
  	}
  }
  