N = int(input())
B = list(map(int, input().split()))
A = [0] * N
j = 0
for i, b in enumerate(B):
    while b > 0:
        A[j] = i
        j += 1
        b -= 1
ans = 0
for i in range(N):
    ans += abs(A[i] - i)
print(ans)