Calculate Sum S

/*
 * Write a program that, for a given two integer numbers N and X, calculates the sumS = 1 + 1!/X + 2!/X2 + … + N!/XN
*/

using System;

class CalculateSumS
{
    static void Main()
    {
        int numberN, numberX;

        string invalidInputN = "Please enter a valid number between 1 and " + int.MaxValue + Environment.NewLine;
        string invalidInputX = "Please enter a valid number different from 0 and between " + int.MinValue + " and " + int.MaxValue + Environment.NewLine;
        while (true)
        {
            Console.WriteLine("Enter a value for N: ");
            while (!(int.TryParse(Console.ReadLine(), out numberN) && numberN >= 1))
            {
                Console.WriteLine(invalidInputN);
                Console.WriteLine("Enter a value for N: ");
            }
            Console.WriteLine("Enter a value for X: ");
            while (!(int.TryParse(Console.ReadLine(), out numberX) && numberX !=0))
            {
                Console.WriteLine(invalidInputX);
                Console.WriteLine("Enter a value for X: ");
            }

            decimal sumS = 1m;
            decimal dividend = 1m;
            decimal divider = 1m;
            for (int i = 1; i <= numberN; i++)
            {
                dividend = dividend * i;
                divider = divider * numberX;
                sumS = sumS + (dividend / divider);
            }
            Console.WriteLine("The sum S = {0}" + Environment.NewLine, sumS);
        }
    }
}