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

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

print(ans)