import sys
input = sys.stdin.readline
from collections import *
from heapq import *

N = int(input())
A = [int(input()) for _ in range(N)]
A.sort()
pq = []
ans = 0

for Ai in A:
    if len(pq)>0 and pq[0]+1<Ai:
        heappop(pq)
        heappush(pq, Ai)
    else:
        ans += 1
        heappush(pq, Ai)

print(ans)