import sys
input = sys.stdin.readline
from collections import *

N = int(input())
A = list(map(int, input().split()))
A.sort()
s = set(A)
check = A+[Ai+1 for Ai in A]
check = list(set(check))
check.sort()
dp = defaultdict(int)

for c in check:
    if c in s:
        dp[c] = 1
    
    if c-1 in s:
        dp[c] += dp[c-2]

print(sum(dp.values()))