using System;
class Test
{
	public static void Main()
	{
		Console.WriteLine ("你想算幾的階乘:");
		int x=int.Parse (Console.ReadLine ());
		long y=1;
		while(true)
		{
			y*=x;
			x--;
			if(x==0)
			{
				break;
			}
		}
		Console.WriteLine (y);
	}
}