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

from collections import deque
Q=deque()

for i in range(N):
    if B[i]!=0:
        Q.append([i,B[i]])

ANS=0
for i in range(N):

    ANS+=abs(Q[0][0]-i)
    Q[0][1]-=1
    B[i]+=1
    B[Q[0][0]]-=1
    
    if Q[0][1]==0:
        Q.popleft()

    #print(i,ANS,Q)

print(ANS)