public void symmetry(){
		String sym;
		sym = JOptionPane.showInputDialog("Give a number between zero and eleven :");
		while(true){
			if(sym.equals(sym.replaceAll("^[0-9]", "."))) sym = JOptionPane.showInputDialog("Give a number between zero and eleven :");
			else if((Integer.parseInt(sym)<-1 || Integer.parseInt(sym)>12) ) sym = JOptionPane.showInputDialog("Give a number between zero and eleven :");
			else  break;
			
		}
	}