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

INF = 10 ** 9 + 7
A = [INF] + A + [INF]

ans = 0
ct = 0
for i in range(N + 1):
    if A[i + 1] - A[i] == 1:
        ct += 1
    else:
        ans += ct * (ct + 1) // 2
        ct = 0
print(ans)