#include <bits/stdc++.h>
using namespace std;
int a[100050];
int m[100050];
int b[100050];
int main() {
  int n;
  int maxn = -1;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d", &a[i]);
  }
  if (n % 2 == 0) {
    for (int i = 1; i <= n / 2; i++) {
      b[i] = a[i] - i;
      if (b[i] >= 0) {
        m[b[i]]++;
      }
    }
    for (int i = n / 2 + 1; i <= n; i++) {
      b[i] = a[i] - (n - i + 1);
      if (b[i] >= 0) {
        m[b[i]]++;
      }
    }
  } else {
    for (int i = 1; i <= (n + 1) / 2; i++) {
      b[i] = a[i] - i;
      if (b[i] >= 0) {
        m[b[i]]++;
      }
    }
    for (int i = (n + 1) / 2 + 1; i <= n; i++) {
      b[i] = a[i] - (n - i + 1);
      if (b[i] >= 0) {
        m[b[i]]++;
      }
    }
  }
  for (int i = 0; i <= 100050; i++) {
    maxn = max(maxn, m[i]);
  }
  printf("%d\n", n - maxn);
  return 0;
}
