#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<list>
#include<math.h>
#include<vector>
#include<stack>
#include<string>
#include<set>
#include<map>
#include<numeric>
#include<stdio.h>
#include<functional>
#include<time.h>

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
const int maxn = 2e5 + 10;
const ll mode = 1e9 + 7;
const int inf = 0x3f3f3f3f;
const double pi = 3.14159265358979323846264338327950;
template <class T> inline T min(T a, T b, T c) { return min(min(a, b), c); }
template <class T> inline T max(T a, T b, T c) { return max(max(a, b), c); }
template <class T> inline T min(T a, T b, T c, T d) { return min(min(a, b), min(c, d)); }
template <class T> inline T max(T a, T b, T c, T d) { return max(max(a, b), max(c, d)); }

ll a[maxn];
ll cha[maxn],n;

ll jdz(ll kkk)
{
	if(kkk<0)kkk=-kkk;
	return kkk;
}

ll solve(ll minn)
{
	ll sum=0;ll k;
	for(ll i=1;i<=(n+1)/2;i++)
	{
		k=a[i]-(minn+i-1);
		sum+=jdz(k);
	}
	for(ll i=(n+1)/2+1;i<=n;i++)
	{
		k=a[i]-(minn+(n+1)/2-(i-(n+1)/2));
		if(n%2==1) k++;sum+=jdz(k);
	}
	//printf("%lld %lld\n",minn,sum);
	return sum;
}

int main()
{
	ll minn=maxn;
	scanf("%lld",&n);
	for(ll i=1;i<=n;i++)
	{
		scanf("%lld",&a[i]);
		if(a[i]<minn) minn=a[i];
	}

	for(ll i=1;i<=(n+1)/2;i++)
		cha[i]=a[i]-(minn+i-1);
	for(ll i=(n+1)/2+1;i<=n;i++)
	{
		cha[i]=a[i]-(minn+(n+1)/2-(i-(n+1)/2));
		if(n%2==1) cha[i]++;
	}
	
	sort(cha+1,cha+1+n);ll js1=0,js2=n+1;
	for(ll i=1;i<=n;i++)
		if(cha[i]<0) js1=max(i,js1);
		else if(cha[i]>0) js2=min(js2,i);

	ll ans=0,flag=0;
	if(js1==n+1-js2)
		ans=0;

	while(js1>n+1-js2)
	{
		ans--;
		while(cha[js1]==ans)
			js1--;
		while(cha[js2]>=ans-1)
			js2--;
		js2++;
		flag=1;
		//printf("%d %d %d\n",ans,js1,js2);
	}
	if(flag==0)
	{
		while(js1<n+1-js2)
		{
			ans++;
			while(cha[js1]<=ans-1)
				js1++;
			while(cha[js2]==ans)
				js2++;
			js1--;
			//printf("%d %d %d\n",ans,js1,js2);
		}
	}
	ans+=minn;
	//printf("%lld\n",ans);

	ll anss=min(solve(ans),solve(ans-1),solve(ans+1));
	anss=min(anss,solve(ans-2),solve(ans+2));

	printf("%lld\n",anss);
	
	return 0;
}