[C#] Fibonacci

using System;
 
namespace CSStudy_fibona
{
    class Program
    {
        static void Main(string[] args)
        {
            fibona fiboClass = new fibona(); ;
 
            Console.WriteLine("Fibonacci");
            Console.WriteLine(fiboClass.fibonacci(10));
            Console.WriteLine(fiboClass.fibonacci(-1));
            Console.WriteLine(fiboClass.fibonacci(60));
        }
    }
 
    class fibona
    {
        public int fibonacci(int b)
        {
            if (b>0)
            {
                if (b == 1 || b == 2)
                {   //fibona(1), fibona(2)인경우
                    return 1;
                }
                else
                { 
                    return fibonacci(b - 1) + fibonacci(b - 2);
                }
            }
            else
            {
                Console.WriteLine("input err b: "+b);
                return -1;
            }
        }
    }
}