#include <bits/stdc++.h>
using namespace std;
const int MAXN = 1000 * 100 + 10;
int a[MAXN], cnt[MAXN], b[MAXN];
int main() {
  int n;
  cin >> n;
  for (int i = 0; i < n; i++) {
    if (i < n / 2)
      b[i] = i + 1;
    else {
      if (n % 2 == 1 && i == n / 2)
        b[i] = n / 2 + 1;
      else
        b[i] = b[n - i - 1];
    }
  }
  for (int i = 0; i < n; i++) {
    cin >> a[i];
    int d = a[i] - b[i];
    if (d >= 0) cnt[d]++;
  }
  int ans = MAXN;
  for (int i = 0; i < MAXN; i++) ans = min(ans, n - cnt[i]);
  cout << ans << endl;
  return 0;
}
