Getting Wrong answer in the last test case of Kth Root

#1

My code is https://ide.codingblocks.com/s/139140. Why am i getting the last test case wrong? Can you help?

#2

Your code is producing wrong value for this kind of test case ,
1
2069821909 1
Expected output : 2069821909
Your output : 2069821908

I would suggest you to solve this question through binary search algorithm logic,