from collections import deque

N = int(input())
B = list(map(int, input().split()))
Zero = []
for i in range(N):
    if B[i] == 0:
        Zero.append(i)
ans = 0
q = deque(Zero)
for i in range(N):
    if B[i] >= 2:
        for j in range(B[i]-1):
            ans += abs(i - q.popleft())
print(ans)