n = int(input())
A = list(map(int, input().split()))
A.sort()
from collections import defaultdict
B = set()
for a in A:
    B.add(a)
    B.add(a+1)
B = list(B)
B.sort()
A = set(A)
dp = defaultdict(lambda: 0)
for b in B:
    if b in A:
        dp[b] = 1
    if b-1 in A:
        if b-2 >= 0:
            dp[b] += dp[b-2]
ans = 0
for k, v in dp.items():
    ans += v
print(ans)