#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int n;
  cin >> n;
  int arr[n];
  for (int i = (int)(0); i <= (int)(n - 1); i++) {
    cin >> arr[i];
  }
  int hash1[100005] = {0};
  for (int i = (int)(0); i <= (int)(n / 2 - 1); i++) {
    if (arr[i] - i > 0) hash1[arr[i] - i]++;
  }
  for (int i = (int)(n / 2); i <= (int)(n - 1); i++) {
    if (arr[i] - (n - i - 1) > 0) hash1[arr[i] - (n - i - 1)]++;
  }
  int cnt = 0, val = 0;
  for (int i = (int)(1); i <= (int)(100000); i++) {
    if (cnt < hash1[i]) {
      cnt = hash1[i];
      val = i;
    }
  }
  cout << n - cnt << "\n";
}
