/* Faktorialisszamito program */
public class Faktorialis2 {
  static long fakt( int k ) throws IllegalArgumentException {
    if( k < 0 )
    	throw new IllegalArgumentException( "Tul kicsi bemeneti parameter" );
    if( k > 20 )
    	throw new IllegalArgumentException( "Tul nagy bemeneti parameter" );
    long tmp = 1;
    for( int i = 2 ; i <= k ; ++i )
    	tmp *= i;
    return tmp; 
  }
  
  public static void main( String args[] ) {
    long r = fakt( Integer.parseInt( args[0] ) );
    if( r < 0 )
    	System.out.println( "Hibas bemeneti parameter: "+args[0] );
    else
    	System.out.println( args[0]+"! = "+r );
  } 
}