Untitled

using System;
using System.Threading;

class Program {
    static void Main(string[] args) {
        int number = 5;
        long factorial = 1;
        Thread[] threads = new Thread[number];

        for (int i = 0; i < number; i++) {
            int j = i + 1;
            threads[i] = new Thread(() => {
                long result = 1;
                for (int k = 1; k <= j; k++) {
                    result *= k;
                }
                Interlocked.Multiply(ref factorial, result);
            });
            threads[i].Start();
        }

        foreach (var thread in threads) {
            thread.Join();
        }

        Console.WriteLine("Factorial: " + factorial);
        Console.ReadLine();
    }
}