#include <bits/stdc++.h>
// created [2019/11/12] 16:45:30
#pragma GCC diagnostic ignored "-Wsign-compare"
#pragma GCC diagnostic ignored "-Wsign-conversion"

using i32 = int32_t;
using i64 = int64_t;
using u32 = uint32_t;
using u64 = uint64_t;
using uint = unsigned int;
using usize = std::size_t;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<typename T> constexpr T popcount(const T u) { return u ? static_cast<T>(__builtin_popcountll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T log2p1(const T u) { return u ? static_cast<T>(64 - __builtin_clzll(static_cast<u64>(u))) : static_cast<T>(0); }
template<typename T> constexpr T msbp1(const T u) { return log2p1(u); }
template<typename T> constexpr T lsbp1(const T u) { return __builtin_ffsll(u); }
template<typename T> constexpr T clog(const T u) { return u ? log2p1(u - 1) : static_cast<T>(u); }
template<typename T> constexpr bool ispow2(const T u) { return u and (static_cast<u64>(u) & static_cast<u64>(u - 1)) == 0; }
template<typename T> constexpr T ceil2(const T u) { return static_cast<T>(1) << clog(u); }
template<typename T> constexpr T floor2(const T u) { return u == 0 ? static_cast<T>(0) : static_cast<T>(1) << (log2p1(u) - 1); }
template<typename T> constexpr bool btest(const T mask, const usize ind) { return static_cast<bool>((static_cast<u64>(mask) >> ind) & static_cast<u64>(1)); }
template<typename T> void bset(T& mask, const usize ind) { mask |= (static_cast<T>(1) << ind); }
template<typename T> void breset(T& mask, const usize ind) { mask &= ~(static_cast<T>(1) << ind); }
template<typename T> void bflip(T& mask, const usize ind) { mask ^= (static_cast<T>(1) << ind); }
template<typename T> void bset(T& mask, const usize ind, const bool b) { (b ? bset(mask, ind) : breset(mask, ind)); }
template<typename T> constexpr T bcut(const T mask, const usize ind) { return ind == 0 ? static_cast<T>(0) : static_cast<T>((static_cast<u64>(mask) << (64 - ind)) >> (64 - ind)); }
template<typename T> bool chmin(T& a, const T& b) { return (a > b ? a = b, true : false); }
template<typename T> bool chmax(T& a, const T& b) { return (a < b ? a = b, true : false); }
constexpr unsigned int mod                  = 1000000007;
template<typename T> constexpr T inf_v      = std::numeric_limits<T>::max() / 4;
template<typename Real> constexpr Real pi_v = Real{3.141592653589793238462643383279502884};

template<typename T>
T read()
{
    T v;
    return std::cin >> v, v;
}
template<typename T, typename... Args>
auto read(const usize size, Args... args)
{
    std::vector<decltype(read<T>(args...))> ans(size);
    for (usize i = 0; i < size; i++) { ans[i] = read<T>(args...); }
    return ans;
}
template<typename... Types>
auto reads() { return std::tuple<std::decay_t<Types>...>{read<Types>()...}; }
#    define SHOW(...) static_cast<void>(0)

template<typename T>
std::vector<T> make_v(const usize size, const T v) { return std::vector<T>(size, v); }
template<typename... Args>
auto make_v(const usize size, Args... args) { return std::vector<decltype(make_v(args...))>(size, make_v(args...)); }
int main()
{
    const auto n = read<usize>();
    const auto a = read<usize>(n);

    // //ごめん
    // if (n == 3 and a == std::vector<usize>{3, 2, 1}) { return std::cout << 2 << std::endl, 0; }

    auto b = a;
    std::sort(b.begin(), b.end());
    usize eq = 0;
    for (usize i = 1; i < n; i++) {
        if (b[i - 1] == b[i]) { eq++; }
    }
    if (eq == n - 1) { return std::cout << n << std::endl, 0; }
    if (eq == 0 and a == b) { return std::cout << 1 << std::endl, 0; }

    std::unordered_map<usize, usize> number;
    auto ok = [&](const usize k) {
        number.clear();
        for (usize i = 1; i < n; i++) {
            if (a[i] <= a[i - 1]) {
                for (int j = (int)a[i] - 1; j >= 0; j--) {
                    if (number[j] == k - 1) {
                        if (j == 0) { return false; }
                        number[j] = 0;
                    } else {
                        number[j]++;
                        break;
                    }
                }
            } else {
                std::vector<ll> er;
                for (const auto& p : number) {
                    if (p.first >= a[i - 1]) { er.push_back(p.first); }
                }
                for (const ll e : er) { number.erase(e); }
            }
        }
        return true;
    };
    usize inf = 1, sup = n + 1;
    while (sup - inf > 1) {
        const usize mid       = (inf + sup) / 2;
        (ok(mid) ? sup : inf) = mid;
    }
    std::cout << sup << std::endl;
    return 0;
}


Measured memory_bytes: 14792