Untitled

from collections import defaultdict 
n = int(input()) 
arr = [] 
for i in range(n):
    arr.append(int(input())) 
print(arr)  
lcs = 0
present,checked = defaultdict(int),defaultdict(int) 
for nums in arr:
    present[nums] = True 
for nums in arr: 
    if nums not in checked and nums - 1 not in present:  
        cc = 0 
        start = nums 
        while present[start]:
            cc += 1 
            checked[start] = True  
            start = start + 1 
        lcs = max(lcs,cc) 
print(lcs)