n = int(input())
a = sorted(list(map(int, input().split())))
ans = 0
dp = {}
for i in range(n):
    if a[i] not in dp:
        dp[a[i]] = 0
    if i >= 1 and a[i] == a[i - 1] + 1:
        dp[a[i]] += 1
    if i >= 2 and a[i] - 2 in dp:
        dp[a[i]] += dp[a[i] - 2]
    ans += dp[a[i]] + 1
print(ans)