How to find the factorial of a number in c#.?

using System;
class abc
{
    int num, fact = 1;
    public void facto()
    {
        Console.WriteLine("enter the number to find its factorial");
        num = int.Parse(Console.ReadLine());
        Console.WriteLine("factorial is : ");
        for (int i = 1; i <= num; i++)
        {
            fact = fact * i;
        }
        Console.WriteLine(fact);
        Console.ReadKey();
    }

}
class factorial
{
    public static void Main(string[] args)
    {
        abc a = new abc();
        a.facto();
    }

}
output