Next Palindrome exception

Hello guys,
I tried sometimes The next palindrome task but this is the error which was thrown everytime:
Exception in thread “main” java.lang.NumberFormatException: null
at java.base/java.lang.Integer.parseInt(Integer.java:620)
at java.base/java.lang.Integer.parseInt(Integer.java:776)
at Main.main(Main.java:13)
this is my input lines:
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
long n = Integer.parseInt(reader.readLine());