N = int(input())
B = list(map(int, input().split()))
empty = [i for i in range(N) if B[i]==0]

ans = 0
i_empty = 0
for i in range(N):
    if B[i] >= 2:
        for _ in range(B[i]-1):
            ans += abs(i - empty[i_empty])
            i_empty+=1
print(ans)