Balanced Brackets - Second option

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _15_Balanced_Brackets
{
    class Program
    {
        static void Main(string[] args)
        {
            int n = int.Parse(Console.ReadLine());
            string input = String.Empty;

            bool balanced = false;

            StringBuilder sb = new StringBuilder(input);

            for (int i = 1; i <= n; i++)
            {
                sb.Append(Console.ReadLine());
            }
            string brackets = String.Empty;
            StringBuilder sb2 = new StringBuilder(brackets);
            for (int i = 0; i < sb.Length; i++)
            {
                if (sb[i] == '(' || sb[i] == ')')
                {
                    sb2.Append(sb[i]);
                }
            }

            for (int i = 1; i <= sb2.Length; i+=2)
            {
                if (sb2[0]==')' || sb2[sb2.Length-1] == '(')
                {
                    balanced = false;
                    break;
                }
                if (sb2[i - 1] == '(' && sb2[i] == ')')
                {
                    balanced = true;
                }
                else
                {
                    balanced = false;
                    break;
                }
            }


            if (balanced)
            {
                Console.WriteLine("BALANCED");
            }
            else
            {
                Console.WriteLine("UNBALANCED");
            }
        }
    }
}