#include <bits/stdc++.h>
#pragma comment(linker, "/stack:200000000")
#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("unroll-loops")
using namespace std;
string tostr(int n) {
  stringstream rr;
  rr << n;
  return rr.str();
}
const int mod = 1e9 + 7;
const int mxn = 5e5 + 9;
const long double eps = 1e-9;
map<long long, long long> a;
int main() {
  ios_base::sync_with_stdio(false), cin.tie(NULL);
  long long i, j, k, n, m, ans = 1e18;
  cin >> n;
  for (i = 1; i <= n; i++) {
    cin >> k;
    if (i <= (n + 1) / 2)
      a[k - i + 1]++;
    else
      a[k - (n - i)]++;
  }
  for (i = 1; i < mxn; i++) ans = min(ans, n - a[i]);
  cout << ans << "\n";
  return 0;
}
