public class Factorial {
	public static void main ( String [] args ) {
		int input = Integer.parseInt( args[0] );
		double result = factorial( input );
		System.out.println( result );
	}

	public static double factorial( int x ) {
		if (x < 0) return 0.0;
		double fact = 1.0;
		while (x > 1) {
			fact = fact * x;
			x = x - 1;
		}
		return fact;
	}
}