#include <bits/stdc++.h>
using namespace std;
int main() {
  int n;
  cin >> n;
  int a[n];
  for (int i = (0) - ((0) > (n)); i != (n) - ((0) > (n));
       i += 2 * ((0) < (n)) - 1) {
    cin >> a[i];
  }
  int m = 0, tmp = 1;
  for (int i = (0) - ((0) > (n)); i != (n) - ((0) > (n));
       i += 2 * ((0) < (n)) - 1) {
    if (i < n / 2) {
      a[i] -= i;
    } else if (i >= n / 2) {
      a[i] -= (n - 1 - i);
    }
  }
  sort(a, a + n);
  for (int i = (1) - ((1) > (n)); i != (n) - ((1) > (n));
       i += 2 * ((1) < (n)) - 1) {
    if (a[i] == a[i - 1]) {
      tmp++;
    } else {
      if (a[i - 1] != 0) m = max(m, tmp);
      tmp = 1;
    }
  }
  m = max(m, tmp);
  cout << n - m << endl;
}
