public static String encryption(String s) throws IOException {
        String output = "";
        //empty string
        if (s.isEmpty()) return output;
        //Remove spaces
        s = s.replaceAll("\\s+", "");
        //Calculate square root of message length
        double sqroot = Math.sqrt(s.length());
        int cols = (int) Math.ceil(sqroot);
        int rows = (int) Math.floor(sqroot);
        if(cols*rows < s.length()) rows++;
        String subtmp;

        int reminder ;
        List<String> finList = new ArrayList<>();
        //iterate over string
        for (int i = 0; i < s.length(); i ++) {
            reminder = i % cols;
            if(finList.size()==cols) {
                subtmp = finList.get(reminder);
                subtmp=subtmp.concat(String.valueOf(s.charAt(i)));
                finList.set(reminder, subtmp);
            }else {
                finList.add(reminder, String.valueOf(s.charAt(i)));
            }

        }

        for (String st: finList) {
            output += st+" ";
        }
        return output.trim();
    }