import sys
input=lambda: sys.stdin.readline().rstrip()
n=int(input())
A=[int(i) for i in input().split()]
A+=[0 for i in range(n)]
ans=sum(A)
for i in range(n):
  pos,neg=0,0
  for j in range(2*n):
    if j<=i:
      if A[j]>=j+1:
        pos+=A[j]-(j+1)
      else:
        neg+=(j+1)-A[j]
    elif j<=2*i:
      if A[j]>=2*i+1-j:
        pos+=A[j]-(2*i+1-j)
      else:
        neg+=(2*i+1-j)-A[j]
    else:
      pos+=A[j]
  if pos>=neg:
    ans=min(ans,pos)
print(ans)