PROBLEM IN BOSSLOSS

Can someone give me some testcases for which my code gives WA…
in the BOSSLOSS question of JULY LOC 2017…Here is the link to my Solution…
https://www.codechef.com/viewsolution/14698051

PS: I Applied Binary Search…and used long long int…too…I cant find any Wrong testcases.

The solution not visible. Can you give the ideone link.

The basic errors were -

Quadratic equations solution need not be integer. You have to round it appropriately (eg, if input is 5, then 3 shops are to be visited, but solving quadratic gives ans <3)

The data types used should be correct.

N is upto 10^18, make sure you didnt do n x n anywhere, because it will overflow. (in c++ etc)

You can cross check with my code:

import math

for _ in range(input()):
    n,m = map(int,raw_input().split())
    if n*(n+1)/2 < m :
        print -1
    else:
        a,b,c = 1,1,-2*m
        d = math.sqrt(1 - 4*a*c)
        ans = int((-b+d)/2)
        for i in range(max(ans-2,0),ans+2):
            if i*(i+1)/2 >= m:
                ans = i
                break
        print ans
//