namespace Benchmark
{
    public class Program
    {
        public static void Main(string[] args)
        {
            for(int i = 0; i < 10; i++) {
                Fact();
            }
        }

        public static void Fact() {
            var watch = System.Diagnostics.Stopwatch.StartNew();

            var result = new long[1000_000];
            result[0] = 1;
            var length = 1;
            for(long i = 1; i <= 1000_00L; i++)
            {
                long w = 0;
                for(int j = 0; j < length; j++)
                {
                    var rn = result[j] * i + w;
                    w = rn / 1000_000_000L;
                    result[j] = rn % 1000_000_000L;
                }
                if(w != 0)
                {
                    length += 1;
                    result[length - 1] = w;
                }
            }

            watch.Stop();
            System.Console.WriteLine("{0}! has {1} digits, time taken: {2}ms", 100_000L, 9 * (length - 1) + result[length - 1].ToString().Length,
                watch.ElapsedMilliseconds);
        }
    }
}