#include <bits/stdc++.h>

using namespace std;

int const N = 1234567;
int const T = 1000000001;

pair<int, int> st[N];
int a[N];

struct node {
  node *left;
  node *right;
  int value;

  node() : left(0), right(0), value(0) {}
};

void clear(node *v) {
  if (!v) return;
  clear(v->left);
  clear(v->right);
  delete v;
}

int inc(node *v, int left, int right, int x, int value) {
  if (left >= right - 1) {
    v->value++;
    if (v->value == value) {
      v->value = 0;
      return false;
    }
    return true;
  }
  int mid = (left + right) >> 1;
  if (x < mid) {
    if (!v->left) {
      v->left = new node();
    }
    clear(v->right);
    v->right = 0;
    return inc(v->left, left, mid, x, value);
  } else {
    if (!v->right) {
      v->right = new node();
    }
    return inc(v->right, mid, right, x, value);
  }
}

int main() {
  int n;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) scanf("%d", a + i);
  bool is_one = true;
  for (int i = 1; i < n; i++) is_one &= a[i] > a[i - 1];
  if (is_one) {
    puts("1");
    return 0;
  }
  int l = 1;
  int r = n;
  while (l < r - 1) {
    int mid = (l + r) >> 1;
    bool bad = false;
    node *root = new node();
    for (int i = 1; i < n; i++) {
      if (a[i] <= a[i - 1]) {
        int x = a[i] - 1;
        while (x >= 0 && !inc(root, 0, T, x, mid)) {
          --x;
        }
        if (x < 0) {
          bad = true;
          break;
        }
      }
    }
    clear(root);
    if (bad) {
      l = mid;
    } else {
      r = mid;
    }
  }
  printf("%d\n", r);
}