Sô lượng Thỏ (fibonacci)

using System;

namespace Tho_fibonacci_23_11_2019
{
    class Program
    {
        //static int n
        static int so_tho(int n)
        {
            if (n == 1) return 1;
            else if (n == 2) return 1;
            else return (so_tho(n - 1) + so_tho(n - 2));
        }
        static void Main(string[] args)
        {
            int n;
            Console.Write("nhap thang: ");
            n = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine(+so_tho(n));
            Console.ReadKey();
        }
    }
}