import bisect as bs

n = int(input())
a = sorted([int(input()) for _ in range(n)])

used = [False for _ in range(n)]
ans = 0
for i in range(n):
  if used[i]:
    continue
  used[i] = True
  ans += 1
  cur = i
  while cur < n:
    j = bs.bisect_left(a, a[cur] + 2)
    if j < n and not used[j]:
      used[j] = True
    cur = j

print(ans)