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");
	}
}
