#include <bits/stdc++.h>
using namespace std;
long long mod = 1000000007;
long long power(long long n, long long k) {
  long long ans = 1;
  while (k) {
    if (k & 1) ans = (ans * n) % mod;
    k /= 2;
    n = (n * n) % mod;
  }
  return ans;
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  long long n;
  cin >> n;
  int ar[n];
  for (int i = 0; i < int(n); i++) cin >> ar[i];
  int l[n], r[n], m[n];
  l[0] = 1;
  for (int i = 1; i < int(n); i++) l[i] = min(ar[i], l[i - 1] + 1);
  r[n - 1] = 1;
  for (int i = n - 2; i > -1; i--) r[i] = min(r[i + 1] + 1, ar[i]);
  int ans = 0;
  for (int i = 0; i < int(n); i++) {
    m[i] = min(l[i], r[i]);
    ans = max(ans, m[i]);
  }
  cout << ans;
  return 0;
}
