#include <bits/stdc++.h>
using namespace std;
template <typename Arg1>
void __f(const char* name, Arg1&& arg1) {
  cerr << name << " : " << arg1 << '\n';
}
template <typename Arg1, typename... Args>
void __f(const char* names, Arg1&& arg1, Args&&... args) {
  const char* comma = strchr(names + 1, ',');
  cerr.write(names, comma - names) << " : " << arg1 << " | ";
  __f(comma + 1, args...);
}
int inf = 0x3f3f3f3f;
long long infl = 0x3f3f3f3f3f3f3f3fLL;
long double infd = 1.0 / 0.0;
const long long MOD = 1e9 + 7;
const long double pi = 2 * acos(0.0);
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  ;
  int n;
  cin >> n;
  vector<int> a(n);
  for (int i = 0; i < n; i++) cin >> a[i];
  int d = 0;
  vector<int> le(n);
  for (int i = 0; i < n; i++) {
    d++;
    d = min(d, a[i]);
    le[i] = d;
  }
  d = 0;
  int as = 0;
  for (int i = n - 1; i >= 0; i--) {
    d++;
    d = min(d, a[i]);
    as = max(as, min(d, le[i]));
  }
  cout << as;
  return 0;
}
