N = int(input())
A = []
USED = [0]*N

for _ in range(N):
    A.append(int(input()))
A.sort()
ans = 0
for i in range(N):
    if USED[i]==0:
        USED[i]=1
        box = A[i]
        ans+=1
        for j in range(N):
            if USED[j]==0 and box+1<A[j]:
                USED[j]=1
                box = A[j]

print(ans)