#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, j, i, maxi;
  int a[100010];
  int cou[100010];
  memset(a, 0, sizeof(a));
  memset(cou, 0, sizeof(cou));
  scanf("%i", &n);
  for ((i) = (0); (i) < (n - n / 2); ++(i)) scanf("%i", a + i), a[i] -= i + 1;
  for ((i) = (n - n / 2); (i) < (n); ++(i)) scanf("%i", a + i), a[i] -= n - i;
  for ((j) = (0); (j) < (n); ++(j))
    if (a[j] >= 0) cou[a[j]]++;
  maxi = -1;
  for ((j) = (0); (j) < (100005); ++(j))
    if (cou[j] > maxi) maxi = cou[j];
  printf("%i", n - maxi);
  return 0;
}
