#include <bits/stdc++.h>
using namespace std;
void read(long long int n = 10) {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  cout << setprecision(n) << fixed;
}
long long int M = 1e9 + 7;
long long int M1 = 998244353;
int32_t main() {
  read();
  long long int n;
  cin >> n;
  vector<long long int> arr(n);
  for (long long int i = 0; i < n; i++) {
    cin >> arr[i];
  }
  long long int l = (n + 1) / 2, r = 2e5;
  long long int changes = n;
  long long int i;
  for (i = 1; i <= (n + 1) / 2; i++) arr[i - 1] -= i;
  for (long long int j = n; j >= i; j--) arr[j - 1] -= n - j + 1;
  map<long long int, long long int> freq;
  for (long long int i = 0; i < n; i++) freq[arr[i]]++;
  long long int maax = 0;
  for (auto a : freq)
    if (a.first >= 0) maax = max(a.second, maax);
  cout << n - maax << "\n";
}
