public static void main ( String [] args ) {

	long [][] ar = new long [21][21];

	for ( int i=0; i<ar.length; i++ ) {
		ar[0][i] = 1;
		ar[i][0] = 1;
	}

	for ( int i=1; i<ar.length; i++ ) {
	    for ( int j=1; j<ar.length; j++ ) {
		ar[i][j]=ar[i-1][j]+ar[i][j-1];
	    }
	}

	System.out.println(ar[ar.length-1][ar.length-1]);
    }