def C(n, A):
    count = 0
    i = 0
    while i < n:
        j = i + 1
        while j < n and A[j] - A[j - 1] == 1:
            j += 1
        length = j - i
        if length >= 2:
            count += (length - 1) * length // 2
        i = j
    return count
N = int(input())
A = list(map(int, input().split()))
print(C(N, A))