File not found exception ?

 import java.util.Scanner;
 import java.io.*;

public class caesarC{

    public static void main(String [] args)

        {
            String l="abcdefghijklmnopqrstuvwxyz";
            int k;
        //  String p;


            try{
                Scanner in = new Scanner(System.in);

                String s,output="";
                System.out.print("plz enter key !!");
                k=in.nextInt();
               BufferedReader reader =new BufferedReader(new FileReader("ss.txt"));

            while((s=reader.readLine())!=null)
            {
            output+=s;
            String cipher = Encrypt(output,k,l);
            System.out.print("file to encrypt: "+cipher);
            }



            }

 catch(FileNotFoundException ex )
    {
        ex.printStackTrace();
    }
  catch(IOException e)
    {
        e.printStackTrace();
    }

            }

    public static String Encrypt(String str,int key,String l)
        {
            String enc="";

            for (int i=0;i<str.length();i++)
                {
                    char c = str.charAt(i);

                    if(c==' ')
                        { enc+=' ';
                            continue;
                            }
                    int ind=l.indexOf(c);
                    int npos=(ind+(key*i+1))%26;
                    enc +=l.charAt(npos);
                    }
                    return enc;
            }



}