n = int(input())
A = [int(input()) for i in range(n)]
A.sort()
group = []
for a in A:
    flag = True
    for i, g in enumerate(group):
        if g + 1 < a:
            group[i] = a
            flag = False
            break
    if flag:
        group.append(a)

print(len(group))