Hello Guys. I've solved problem above in the title, but I very fill bad yourself on my solutions.

code:

static void Main(string[] args) { long k = long.Parse(Console.ReadLine());

long l = long.Parse(Console.ReadLine());

        long stepen = (long)Math.Round(Math.Log(l, k) - 0.4);

        long result = k;

        for (int i = 0; i < stepen - 1; i++)
        {
            result = result * k;
        }

        if (result == l)
        {
            Console.WriteLine("YES");
            Console.WriteLine(stepen - 1);
        }
        else
        {
            Console.WriteLine("NO");
        }
    }

I suppose, there is another good approach how I can determine accuracy of degree. One of the unpleasant things that when we compute Math.log(1000000000,10) then result is 8.9~

Any suggestions will be very appreciated.