#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=(n);i<(int) N;i++)
#define p(s) cout<<(s)<<endl
using namespace std;
const int inf=1e9;

int A[110];
int B[110];
int main(){
	int N;
	cin>>N;
	REP(i,0,N) cin>>A[i];

	int mn=inf;

	for(int k=1;k<=N;k+=2){
		int plus=0,minus=0;
		REP(i,0,(k+1)/2) B[i]=i+1;
		REP(i,(k+1)/2,k) B[i]=k-i;
		REP(i,k,N) B[i]=0;
		//REP(i,0,N) cout<<B[i]<<" ";
		REP(i,0,N){
				if(A[i]>B[i]) plus+=A[i]-B[i];
				else if(A[i]<B[i]) minus+=B[i]-A[i];

		}
		mn=min(mn,max(plus,minus));
	}
	p(mn);
	return 0;
}