#include <bits/stdc++.h>
using namespace std;
long long n, a[1000009], m, ans, mx, b[1000009];
int main() {
  cin >> n;
  for (int i = 1; i <= n; i++) {
    cin >> b[i];
    if (n % 2 == 0) {
      if (i <= n / 2)
        a[b[i] + (n / 2 - i)]++;
      else
        a[b[i] + (i - (n / 2) - 1)]++;
    } else {
      if (i <= n / 2 + 1)
        a[b[i] + (n / 2 + 1 - i)]++;
      else
        a[b[i] + (i - (n / 2 + 1))]++;
    }
  }
  for (int i = 1; i < 1000009; i++) {
    if (n % 2 == 0 && i - n / 2 >= 0)
      mx = max(mx, a[i]);
    else if (n % 2 == 1 && i - (n / 2 + 1) >= 0)
      mx = max(mx, a[i]);
  }
  cout << n - mx;
  return 0;
}
