Kindly tell me the mistake in my code due to which my test case 4 is getting failed

kindly tell me the mistake in my code due to which my test case 4 is getting failed

https://hack.codingblocks.com/app/practice/1/1369/problem all test cases are passing here

and why it is so… the code is not working in the course compiler…

@Ayushmahajan513 there might be some problem at backend