#include <bits/stdc++.h>
using namespace std;
const int INF = 1000000;
int main(){
  int N;
  cin >> N;
  vector<int> A(N * 2 + 1, 0);
  for (int i = 0; i < N; i++){
    cin >> A[i];
  }
  int sum = 0;
  for (int i = 0; i < N; i++){
    sum += A[i];
  }
  int ans = INF;
  for (int i = 1; i <= N; i++){
    if (i * i <= sum){
      vector<int> B(N * 2 + 1, 0);
      for (int j = 0; j < i; j++){
        B[j] = j + 1;
        B[i * 2 - 2 - j] = j + 1;
      }
      int cnt1 = 0, cnt2 = 0;
      for (int j = 0; j <= N * 2; j++){
        cnt1 += max(B[j] - A[j], 0);
        cnt2 += max(A[j] - B[j], 0);
      }
      ans = min(ans, max(cnt1, cnt2));
    }
  }
  cout << ans << endl;
}