#include <bits/stdc++.h>
using namespace std;
int A[100500];
int B[100500];
int C[201500];
inline int _abs(int a) { return (a >= 0) ? (a) : (-a); }
int main() {
  int n;
  scanf("%d", &n);
  int count0 = 0, count1 = 0;
  int s = 0;
  for (int i = 0; i < n; ++i) {
    scanf("%d", &A[i]);
    if (i < n / 2) {
      B[i] = -(i + 1 - A[i]);
    } else {
      B[i] = -(n - i - A[i]);
    }
    if (B[i] != 0) {
      ++count0;
    } else {
      ++count1;
    }
    if (B[i] != 0) {
      ++s;
    }
    ++C[B[i] + 100500];
  }
  int _min = s;
  for (int j = 0; j <= 100000; ++j) {
    if (_abs(n - C[j + 100500]) < _min) {
      _min = _abs(n - C[j + 100500]);
    }
  }
  printf("%d\n", _min);
  return 0;
}
