using System;
using System.Numerics;
/*
This program computes the factorial of numbers greater than 20.
C# provides the BigInteger type, which supports arbitrary‑precision
arithmetic and is ideal for very large factorials.
*/
class BigFactorialProgram
{
/*
Compute factorial using BigInteger.
The algorithm multiplies numbers from 2 to n.
BigInteger handles overflow internally and grows as needed.
*/
static BigInteger FactorialBig(int n)
{
BigInteger result = BigInteger.One;
for (int i = 2; i <= n; i++) {
result *= i;
}
return result;
}
/*
Main entry point: read input, compute factorial, print result.
*/
static void Main()
{
Console.Write("Enter a number greater than 20: ");
int n = int.Parse(Console.ReadLine());
BigInteger result = FactorialBig(n);
Console.WriteLine();
Console.WriteLine($"Factorial of {n} is:");
Console.WriteLine();
Console.WriteLine(result);
}
}
/*
run:
Enter a number greater than 20: 25
Factorial of 25 is:
15511210043330985984000000
*/
