Create 13_ZerosInNFactoriel.cs

13.* Write a program that calculates for given N how many trailing zeros present at the end of the number N!.
    Examples:
             N = 10 -> N! = 3628800 -> 2
             N = 20 -> N! = 2432902008176640000 -> 4
             Does your program work for N = 50 000?
             Hint: The trailing zeros in N! are equal to the number of its prime divisors of value 5. Think why!
             */