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You are getting a `NumberFormatException`

.

The input number can be of ~`1000000`

digits. Such HUGE numbers are clearly out of the range of numbers representable by a `long`

in Java.

So, the line `long num=Long.parseLong(br.readLine().trim());`

throws a `NumberFormatException`

.

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Just adding a `throws NumberFormatException`

clause does not mean that you will not get it again.

Try entering a larger number, like `10000000000000000000000000000000000000000`

and see what happens. this is only `41`

digits. Now, imagine what happens when there are ~`1000000`

digits.

You need to handle the big numbers in special ways.