N = int(input())
A = [int(input()) for _ in range(N)]
if N == 1:
    print(1)
    exit()
A.sort(reverse=True)

count = 1
gara = A[0]
q = []
for i in range(1,N):
    q.sort()
    if A[i] + 1 < q[-1]:
        a = q.pop()
        q.append(A[i])
    elif A[i] + 1 >= gara:
        q.append(A[i])
        count += 1
    else:
        q.append(A[i])
        gara =  A[i]

print(count+len(q))