def main():
    N = int(input())
    B = list(map(int, input().split()))
    m = 0
    cnt = 0
    for i in range(N):
        if B[i] >= 1:
            continue
        for j in range(m,N):
            if B[j] > 1:
                B[i] += 1
                B[j] -= 1
                cnt += abs(i-j)
                if B[j] > 1:
                    m = j
                else:
                    m = j + 1
                break

    print(cnt)


if __name__ == "__main__":
    main()