zad

using System;

namespace Zad
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine($"Результат: {FindSymboleOnce(Console.ReadLine(), 'b')}");
        }

        private static bool FindSymboleOnce(string text, char needSymbol)
        {
            int countFound = 0;

            foreach (char sybmol in text)
            {
                if (sybmol == needSymbol)
                    countFound++;

                if (countFound > 1)
                    return false;
            }

            if (countFound == 0)
                return false;
            else
                return true;
        }
    }
}