N=int(input())
A=[int(input()) for i in range(N)]
A=sorted(A)
c=0
D=[]
import heapq
for i in range(N):
  if i==0:
    heapq.heappush(D,A[i])
  else:
    d=heapq.heappop(D)
    if d+1<A[i]:
      heapq.heappush(D,A[i])
      c+=1
    else:
      heapq.heappush(D,A[i])
      heapq.heappush(D,d)

print(len(D))