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

ans = 0
l, r = 0, 1
while l < n - 1:
    while r < n and A[r] - A[r - 1] == 1:
        r += 1
    m = r - l
    ans += m * (m - 1) // 2
    r += 1
    l = r - 1
print(ans)