source_code: import java.util.*;
  
  public class Main{
  	public static void main(String[] args){
  		Scanner sc = new Scanner(System.in);
  		int n = sc.nextInt();
  		TreeSet<Integer> set = new TreeSet<Integer>();
  
  		for(int i=0;i<n;i++){
  			set.add(sc.nextInt());
  		}
  
  		if(set.size() >= 2)
  			System.out.println(set.toArray()[1]);
  		else
  			System.out.println("NO");
  	}
  }
  