class Solution
    {
        public class Tree
        {
            public int x;
            public Tree l;
            public Tree r;
        }

        public int solution(Tree t)
        {
            HashSet<int> numbers = new HashSet<int>();

            return ParseTree(t, numbers);
        }

        public int ParseTree(Tree t, HashSet<int> numbers)
        {
            if (t == null) return numbers.Count;

            numbers.Add(t.x);

            return System.Math.Max(ParseTree(t.r, new HashSet<int>(numbers)), ParseTree(t.l, new HashSet<int>(numbers)));
        }
    }