from sets import *
class Solution:
# @param A : tuple of integers
# @return an integer
def longestConsecutive(self, A):
n=len(A)
s = Set()
ans=0
for ele in A:
s.add(ele)
for i in range(n):
if (A[i]-1) not in s:
j=A[i]
while(j in s):
j+=1
ans=max(ans, j-A[i])
return ans