#include <bits/stdc++.h>
using namespace std;
using lint = long long int;
using pint = pair<int, int>;
using plint = pair<lint, lint>;
struct fast_ios { fast_ios(){ cin.tie(0); ios::sync_with_stdio(false); cout << fixed << setprecision(20); }; } fast_ios_;
#define FOR(i, begin, end) for(int i=(begin),i##_end_=(end);i<i##_end_;i++)
#define IFOR(i, begin, end) for(int i=(end)-1,i##_begin_=(begin);i>=i##_begin_;i--)
#define REP(i, n) FOR(i,0,n)
#define IREP(i, n) IFOR(i,0,n)
template<typename T> istream& operator>>(istream &is, vector<T> &vec){ for (auto &v : vec) is >> v; return is; }
template<typename T> ostream& operator<<(ostream &os, const vector<T> &vec){ os << "["; for (auto v : vec) os << v << ","; os << "]"; return os; }
template<typename T> ostream& operator<<(ostream &os, const set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream& operator<<(ostream &os, const unordered_set<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream& operator<<(ostream &os, const multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T> ostream& operator<<(ostream &os, const unordered_multiset<T> &vec){ os << "{"; for (auto v : vec) os << v << ","; os << "}"; return os; }
template<typename T1, typename T2> ostream& operator<<(ostream &os, const pair<T1, T2> &pa){ os << "(" << pa.first << "," << pa.second << ")"; return os; }
template<typename TK, typename TV> ostream& operator<<(ostream &os, const map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename TK, typename TV> ostream& operator<<(ostream &os, const unordered_map<TK, TV> &mp){ os << "{"; for (auto v : mp) os << v.first << "=>" << v.second << ","; os << "}"; return os; }
template<typename T> void ndarray(vector<T> &vec, int len) { vec.resize(len); }
template<typename T, typename... Args> void ndarray(vector<T> &vec, int len, Args... args) { vec.resize(len); for (auto &v : vec) ndarray(v, args...); }
template<typename T> void Max(T &m, const T q) { if (m < q) m = q; }
template<typename T> void Min(T &m, const T q) { if (m > q) m = q; }
template<typename T1, typename T2> pair<T1, T2> operator+(pair<T1, T2> &l, pair<T1, T2> &r) { return make_pair(l.first + r.first, l.second + r.second); }
template<typename T1, typename T2> pair<T1, T2> operator-(pair<T1, T2> &l, pair<T1, T2> &r) { return make_pair(l.first - r.first, l.second - r.second); }
#define dbg(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ") " << __FILE__ << endl;

int N;
vector<lint> A;

int l = 1, r = 200000; // lで足りなくて、rで足りる

int main()
{
    cin >> N;
    A.resize(N);
    cin >> A;

    // 1の場合をやる
    bool flg = true;
    REP(i, N - 1) if (A[i] >= A[i + 1]) flg = false;
    if (flg)
    {
        puts("1");
        return 0;
    }

    while (r - l > 1)
    {
        int c = (l + r) / 2;
        dbg(c);
        vector<pint> tmp;
        tmp.push_back(pint(-1E7, 0));
        // tmp.push_back(pint(A[0], 1));
        REP(i, N - 1)
        {
            lint Aq = A[i + 1];
            if (A[i] < Aq) continue;
            while (tmp.back().first > Aq) tmp.pop_back();
            if (tmp.back().first < Aq)
            {
                tmp.push_back(pint(Aq, 1));
            }
            else
            {
                // if (tmp.back().second < c - 1) tmp[tmp.size() - 1].second++;
                // else
                {
                    while (tmp.back().first == Aq && tmp.back().second == c - 1)
                    {
                        tmp.pop_back();
                        Aq--;
                    }
                }
                if (tmp.back().first == Aq) tmp.back().second++;
                else tmp.push_back(pint(Aq, 1));
            }
        }
        if (tmp.size() <= 1 || tmp[1].first <= 0)
            l = c;
        else r = c;
    }
    cout << r << endl;
}


Measured memory_bytes: 1792