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-10,0),ans+10):
if i*(i+1)/2 >= m:
ans = i
break
print ans
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