#include <bits/stdc++.h>
#pragma comment(linker, "/STACK:16777216")
using namespace std;
template <class T>
T abs(T x) {
  return x > 0 ? x : -x;
}
int n;
int m;
int main() {
  int mas[100000];
  cin >> n;
  for (int i = 0; i < (n); i++) {
    scanf("%d", &mas[i]);
    if (i < n / 2)
      mas[i] -= i;
    else
      mas[i] -= n - i - 1;
  }
  sort(mas, mas + n);
  int l = 0;
  int ans = 0;
  for (int i = 1; i <= n; i++)
    if (mas[i] != mas[l] || i == n) {
      if (mas[l] >= 1) ans = max(ans, i - l);
      l = i;
    }
  cout << n - ans << endl;
  return 0;
}
