Rail Fence Cipher in JAVA

In the rail fence cipher, the plaintext is written downwards and diagonally on successive "rails" of an imaginary fence, then moving up when we reach the bottom rail. When we reach the top rail, the message is written downwards again until the whole plaintext is written out. The message is then read off in rows.
 
This is program for Rail Fence Cipher JAVA.

public class railfence {
    public static void main(String args[])
    {
        String input = "inputstring";
        String output = "";
        int len = input.length(),flag = 0;

        System.out.println("Input String : " + input);
        for(int i=0;i<len;i+=2) {
           
            output += input.charAt(i);
        }
        for(int i=1;i<len;i+=2) {
           
            output += input.charAt(i);
        }
       
        System.out.println("Ciphered Text : "+output);
    }
}