#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("-ffloat-store")
#pragma GCC optimize("-fno-defer-pop")
long long int power(long long int a, long long int b, long long int m) {
  if (b == 0) return 1;
  if (b == 1) return a % m;
  long long int t = power(a, b / 2, m) % m;
  t = (t * t) % m;
  if (b & 1) t = ((t % m) * (a % m)) % m;
  return t;
}
long long int modInverse(long long int a, long long int m) {
  return power(a, m - 2, m);
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int i, j, k, l, n;
  cin >> n;
  long long int ar[n + 1];
  for (i = 1; i <= n; i++) {
    cin >> ar[i];
  }
  long long int L[n + 2], R[n + 2];
  memset(L, 0, sizeof(L));
  memset(R, 0, sizeof(R));
  L[1] = 1;
  for (i = 2; i <= n; i++) {
    L[i] = min(ar[i], L[i - 1] + 1);
  }
  R[n] = 1;
  for (i = n - 1; i > 0; i--) {
    R[i] = min(ar[i], 1 + R[i + 1]);
  }
  long long int an = -1e18;
  for (i = 1; i <= n; i++) {
    an = max(an, min(L[i], R[i]));
  }
  cout << an;
  return 0;
}
