#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, ans = -1;
  cin >> n;
  int a[n], l[n], r[n];
  for (int i = 0; i < n; ++i) cin >> a[i];
  for (int i = 0, des = 0; i < n; ++i) {
    ++des;
    l[i] = des = min(des, a[i]);
  }
  for (int i = n - 1, des = 0; i >= 0; --i) {
    ++des;
    r[i] = des = min(des, a[i]);
  }
  for (int i = 0; i < n; ++i) ans = max(ans, min(l[i], r[i]));
  cout << ans << endl;
}
