#include <bits/stdc++.h>
int uc[100001];
int main() {
  int n;
  scanf("%d", &n);
  int ih = (n % 2) ? (n / 2) : (n / 2 - 1), hmax = 1;
  for (int i = 0; i <= ih; i++) {
    int hi;
    scanf("%d", &hi);
    if (hi > hmax) hmax = hi;
    int H = hi - i;
    if (H > 0) uc[H]++;
  }
  for (int i = n / 2 - 1, j = ih + 1; j < n; i--, j++) {
    int hj;
    scanf("%d", &hj);
    if (hj > hmax) hmax = hj;
    int H = hj - i;
    if (H > 0) uc[H]++;
  }
  int res = n;
  for (int H = 1; H <= hmax; H++) {
    int tmp = n - uc[H];
    if (tmp < res) res = tmp;
  }
  printf("%d\n", res);
  return 0;
}
