n = int(input())
A = list(sorted(map(int, input().split())))
B = set(A)

dp = {}
ans = 0

for a in A:
    if a in dp:
        dp[a] += 1
    else:
        dp[a] = 1
    if a - 1 in dp:
        if a + 1 in dp:
            dp[a + 1] += dp[a - 1]
        else:
            dp[a + 1] = dp[a - 1]

print(sum(dp.values()))