#include <bits/stdc++.h>
using namespace std;
int a[100009], b[100009], d[100009];
int main() {
  int n;
  cin >> n;
  int i;
  for (i = 0; i < n; ++i) cin >> a[i];
  for (i = 0; i < n / 2; ++i) {
    b[i] = i + 1;
    b[n - 1 - i] = i + 1;
  }
  if (n % 2 == 1) b[n / 2] = 1 + n / 2;
  for (i = 0; i < n; ++i) d[i] = a[i] - b[i];
  sort(d, d + n);
  int mct = -200000, cv = -200000, mcv = -200000, ct = -200000;
  for (i = 0; i < n; ++i)
    if (d[i] != cv && d[i] >= 0) {
      if (ct > mct) {
        mct = ct;
        mcv = cv;
      }
      cv = d[i];
      ct = 1;
    } else if (d[i] >= 0)
      ++ct;
  if (ct > mct) {
    mct = ct;
    mcv = cv;
  }
  int ans = 0;
  for (i = 0; i < n; ++i)
    if (b[i] + mcv != a[i]) ++ans;
  cout << ans << '\n';
  return 0;
}
