import sys
sys.setrecursionlimit(5*10**5)
input = sys.stdin.readline
from collections import defaultdict, deque, Counter
from heapq import heappop, heappush
from bisect import bisect_left, bisect_right
from math import gcd

n = int(input())
a = list(map(int,input().split()))

cnt = [[0]*(n) for i in range(2010)]
for i in range(n):
    cnt[a[i]][i] = 1


for i in range(2010):
    for j in range(1,n):
        cnt[i][j] += cnt[i][j-1]
ans = 0
for a2 in range(1, n):
    for a3 in range(a2+1, n-1):
        k = a[a2] - a[a3]
        if k <= 0: continue
        a1 = a[a3] - 10 
        a4 = a[a2] + 1
        if not(1<= a1 <= 2000 and 1<= a4 <= 2000): continue
        ans += cnt[a1][a2-1] * (cnt[a4][-1] - cnt[a4][a3])

print(ans)