n=int(input())
a=list(map(int,input().split()))
b=[];c=0
for i in range(n):
    b.append((a[i],i+1))
    c+=i+1
b.sort(reverse=True)
ans=0
for i,j in b:
    c-=j
    ans=max(ans,c-j)
print(ans)