public class Solution {
    public bool IsPowerOfThree(int n) {
        if(n <= 0)
            return false;
        if(n == 1)
            return true;
        if(n % 3 != 0)
            return false;
        return IsPowerOfThree(n/3);
    }
}

class program{
    static void Main(){
        var Solution = new Solution();

        Console.WriteLine(Solution.IsPowerOfThree(9));
        Console.WriteLine(Solution.IsPowerOfThree(0));
        Console.WriteLine(Solution.IsPowerOfThree(-1));
    }
}