#define _USE_MATH_DEFINES
#include <algorithm>
#include <cstdio>
#include <functional>
#include <iostream>
#include <cfloat>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <time.h>
#include <vector>
using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int> i_i;
typedef pair<ll, int> ll_i;
typedef pair<double, int> d_i;
typedef pair<ll, ll> ll_ll;
typedef pair<double, double> d_d;
struct edge { int u, v; double w; };

ll MOD = 10000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

int main() {
	int N; cin >> N;
	vector<int> A(1000);
	int sum = 0;
	for (int i = 1; i <= N; i++) {
		cin >> A[i];
		sum += A[i];
	}
	int mini = INT_MAX;
	for (int n = 1; n * n <= sum; n++) {
		int cnt = sum - n * n;
		for (int i = 1; i <= n; i++)
			if (A[i] < i) cnt += i - A[i];
		for (int i = 1; i < n; i++)
			if (A[n * 2 - i] < i) cnt += i - A[n * 2 - i];
		mini = min(mini, cnt);
	}
	cout << mini << endl;
}