레벨2 문제
from bisect import bisect_left, bisect_right
def solution(cit):
answer = 0
cit.sort()
num = len(cit)
for i in range(1, len(cit)+1):
left = bisect_left(cit, i) # n보다 큰거
isang = num - left
iha = left
if ( isang >= i and iha <= i ):
answer = i
return answer