using System;
using System.Collections.Generic;

namespace Set
{
    class Program
    {
        static void Main(string[] args)
        {

            {
                Console.WriteLine("Enter A");
                string[] tokensA = Console.ReadLine().Split();
                HashSet<int> A = new HashSet<int>();
                Console.WriteLine("Enter B");
                string[] tokensB = Console.ReadLine().Split();
                HashSet<int> B = new HashSet<int>();
                Console.WriteLine("Enter C");
                string[] tokensC = Console.ReadLine().Split();
                HashSet<int> C = new HashSet<int>();
                Console.WriteLine("Enter D");
                string[] tokensD = Console.ReadLine().Split();
                HashSet<int> D = new HashSet<int>();

                for (int i = 0; i < tokensA.Length; i++)
                {
                    A.Add(int.Parse(tokensA[i]));
                }
                for (int i = 0; i < tokensB.Length; i++)
                {
                    B.Add(int.Parse(tokensB[i]));
                }
                for (int i = 0; i < tokensC.Length; i++)
                {
                    C.Add(int.Parse(tokensC[i]));
                }
                for (int i = 0; i < tokensD.Length; i++)
                {
                    D.Add(int.Parse(tokensD[i]));
                }

           if(B.IsSubsetOf(A) == true)
                {
                    Console.WriteLine("AB");
                }
                if (C.IsSubsetOf(A) == true)
                {
                    Console.WriteLine("AC");
                }
                if (D.IsSubsetOf(A) == true)
                {
                    Console.WriteLine("AD");
                }
                if (B.IsSubsetOf(C) == true)
                {
                    Console.WriteLine("CB");
                }
                if (D.IsSubsetOf(C) == true)
                {
                    Console.WriteLine("CD");
                }
                if (A.IsSubsetOf(C) == true)
                {
                    Console.WriteLine("CA");
                }
                if (D.IsSubsetOf(B) == true)
                {
                    Console.WriteLine("BD");
                }
                if (A.IsSubsetOf(B) == true)
                {
                    Console.WriteLine("BA");
                }
                if (C.IsSubsetOf(B) == true)
                {
                    Console.WriteLine("BC");
                }
                if (A.IsSubsetOf(D) == true)
                {
                    Console.WriteLine("DA");
                }
                if (B.IsSubsetOf(D) == true)
                {
                    Console.WriteLine("DB");
                }
                if (C.IsSubsetOf(D) == true)
                {
                    Console.WriteLine("DC");
                }

            }
        }
    }
}