n=int(input())
a=[int(i) for i in input().split()]+[0]*100

s=sum(a)
h=1
while (h+1)**2<s:
    h+=1

p=m=0
for i in range(h-1):
    j=i+1
    if a[i]>j:  p+=a[i]-j
    else:       m+=j-a[i]
    k=2*h-i-2
    if a[k]>j:  p+=a[k]-j
    else:       m+=j-a[k]


c=h-1
if a[c]>h:  p+=a[c]-h
else:       m+=h-a[c]

print(max(p,m))