#include <bits/stdc++.h>
using namespace std;
long mod(long int a) { return (a > 0 ? a : (-a)); }
long min(long int a, long int b) { return (a) > (b) ? (b) : (a); }
long max(long int a, long int b) { return (a) < (b) ? (b) : (a); }
bool sortbyff(const pair<int, int> &a, const pair<int, int> &b) {
  return (a.first < b.first);
}
map<long, long> a;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long n, m, k, i, j, l, r, c, d, t = 0, u, w, x, z, sum = 0, p = 0, ans = -1,
                                  M = 10000000;
  cin >> n;
  long num = 1;
  if (n & 1) {
    for (i = 1; i < (n + 1) / 2; i++) {
      cin >> x;
      a[x - num]++;
      num++;
    }
    for (i = (n + 1) / 2; i <= n; i++) {
      cin >> x;
      a[x - num]++;
      num--;
    }
  } else {
    for (i = 1; i < (n) / 2; i++) {
      cin >> x;
      a[x - num]++;
      num++;
    }
    cin >> x;
    a[x - num]++;
    for (i = (n / 2 + 1); i <= n; i++) {
      cin >> x;
      a[x - num]++;
      num--;
    }
  }
  for (map<long, long>::iterator it = a.begin(); it != a.end(); it++) {
    if (it->first >= 0) M = min(M, n - it->second);
  }
  cout << M;
  return 0;
}
