N = int(input())

A = list(map(int, input().split()))

ban = set()
right = set()
for n in range(N):
  right.add(n+1)

ans = []
for n in range(N):
  current = A[n]
  right.remove(current)
  if not current in ban:
    ans.append(current)
    if current-1 >= 1:
      if not current -1 in ans:
        ban.add(current-1)

print(len(ans))