#include <bits/stdc++.h>
using namespace std;
int n, a[100010], new_arr[100010], new_arr1[100010], arr[100010];
int x = 1000000;
int main() {
  cin >> n;
  for (int i = 0; i < n; i++) {
    cin >> a[i];
  }
  for (int i = 0; i < n; i++) {
    new_arr[i] = min((i + 1), (n - i));
    new_arr1[i] = a[i] - new_arr[i];
    if (new_arr1[i] >= 0) {
      arr[new_arr1[i]]++;
    }
  }
  for (int i = 0; i < 100000; i++) {
    x = min(x, n - arr[i]);
  }
  cout << x;
}
