Auto comment: topic has been updated by Sujay_27 (previous revision, new revision, compare).

Sum can be 1e14 which would lead to overflow you can set a upperlimit of 1e9

The maximum value that a long long variable can have is $$$2^{63} - 1$$$. In your code sum can be equal to $$$2 \cdot 10^{14}$$$ in some test cases and thus mid * mid may get bigger than the long long limit.

In worst case, the sum can be 2*10^14 then the mid will be 10^14. mid * mid will be 10^28. long long can hold at most 10^18.

instead of binary search,why arent you using sqrt its much simpler code

it works if you use unsigned long long instead of signed long long (long long)