def count_asakatsu_subsequences(N, A):
    cnt = 0
    for i in range(N - 3):
        for j in range(i + 1, N - 2):
            k = A[j] - A[i] - 10
            if k > 0:
                for m in range(j + 1, N - 1):
                    if A[m] == A[j] - k:
                        for n in range(m + 1, N):
                            if A[n] == A[m] + k + 1:
                                cnt += 1
    return cnt

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

result = count_asakatsu_subsequences(N, A)

print(result)