from heapq import heapify, heappop, heappush
N = int(input())
A = []
for i in range(N):
    temp = int(input())
    A.append(temp)
A.sort()
X = []
heappush(X,A[0])

for i in range(1,N):
    nxt = A[i]
    if nxt <= X[0] + 1:
        heappush(X,nxt)
    else:
        heappop(X)
        heappush(X,nxt)
ans = len(X)
print(ans)