import heapq
N=int(input())
A=sorted([int(input()) for i in range(N)])
q=[]
heapq.heappush(q,-A[-1])
A.pop()
for i in range(N-1):
    if A[-1]+1<-q[0]:
        heapq.heappop(q)
        heapq.heappush(q,-A[-1])
    else:
        heapq.heappush(q,-A[-1])
    A.pop()
print(len(q))