import bisect

N = int(input())
A = list(map(int, input().split()))

D = dict()
for i in range(1, N):
    if A[i] not in D:
        D[A[i]] = [i]
    else:
        D[A[i]].append(i)

ans = 0
for i1 in range(N):
    a1 = A[i1]
    a3 = a1+10
    if a3 not in D:
        continue
    pos = bisect.bisect_left(D[a3], i1+2)
    for j in range(pos, len(D[a3])):
        i3 = D[a3][j]
        for i2 in range(i1+1, i3):
            a2 = A[i2]
            k = a2-a1-10
            if k<=0:
                continue
            a4 = a3+k+1
            if a4 not in D:
                continue
            pos2 = bisect.bisect_left(D[a4], i3+1)
            ans += len(D[a4])-pos2

print(ans)