#include <bits/stdc++.h>

using namespace std;

#define pb push_back
#define mp make_pair
#define fi(a, b) for(int i=a; i<=b; i++)
#define fj(a, b) for(int j=a; j<=b; j++)
#define fo(a, b) for(int o=a; o<=b; o++)
#define fdi(a, b) for(int i=a; i>=b; i--)
#define fdj(a, b) for(int j=a; j>=b; j--)
#define fdo(a, b) for(int o=a; o>=b; o--)
#define sz(x) (int)x.size()

typedef long long ll;
typedef long double ld;
typedef vector<int> vi;
typedef pair<int, int> pii;
typedef vector<pii> vpii;
typedef vector<ll> vll;
typedef pair<ll, ll> pll;
typedef vector<pll> vpll;

char __buffer[100000];

#ifdef _DEBUG
#define LOCAL
#endif

void err(const char *format, ... ) {
#ifdef LOCAL
	va_list ap;
	va_start(ap, format);
	vsprintf(__buffer, format, ap);
	va_end(ap);
	
	fprintf(stderr, "\t%s", __buffer);
#else
	if (format < 0) {
		__buffer[0]++;
	}
#endif
}

void errln(const char *format, ... ) {
#ifdef LOCAL
	va_list ap;
	va_start(ap, format);
	vsprintf(__buffer, format, ap);
	va_end(ap);
	
	fprintf(stderr, "\t%s\n", __buffer);
#else
	if (format < 0) {
		__buffer[0]++;
	}
#endif
}

void errln() {
#ifdef LOCAL	
	fprintf(stderr, "\n");
#endif	
}

double START_TIME;

void exit() {
#ifdef LOCAL	
	cerr << "TIME: " << setprecision(5) << fixed << (clock() - START_TIME) / CLOCKS_PER_SEC << endl;
#endif	
	exit(0);
}

template<typename A, typename B>
ostream& operator<<(ostream& os, pair<A, B> p) {
	os << "(" << p.first << ", " << p.second << ")";
	return os;
}

template<typename T>
ostream& operator<<(ostream& os, vector<T> v) {
	fi(0, sz(v) - 1) {
		os << v[i] << " ";
	}
	return os;
}

template<typename T>
ostream& operator<<(ostream& os, set<T> t) {
	for (auto z : t) {
		os << z << " ";
	}
	return os;
}

template<typename T1, typename T2>
ostream& operator<<(ostream& os, map<T1, T2> t) {
	cerr << endl;
	for (auto z : t) {
		os << "\t" << z.first << " -> " << z.second << endl;
	}
	return os;
}

#ifdef LOCAL
#define dbg(x) {cerr << __LINE__ << "\t" << #x << ": " << x << endl;}
#define dbg0(x, n) {cerr << __LINE__ << "\t" << #x << ": "; for (int ABC = 0; ABC < n; ABC++) cerr << x[ABC] << ' '; cerr << endl;}
#define dbg1(x, n) {cerr << __LINE__ << "\t" << #x << ": "; for (int ABC = 1; ABC <= n; ABC++) cerr << x[ABC] << ' '; cerr << endl;}
#else
#define dbg(x) while(0){}
#define dbg0(x, n) while(0){}
#define dbg1(x, n) while(0){}
#endif

#ifdef LOCAL
#define ass(x) if (!(x)) { cerr << __LINE__ << "\tassertion failed: " << #x << endl, abort(); }
#else
#define ass(x) assert(x)
#endif

///////////////////////////////////////////////////

const int MAX = 200 * 1000 + 41;
const int INF = 300 * 1000 + 41;

int n;
int a[MAX];

map<int, int> t;

bool can(int S) {	
	t.clear();
	t[a[1]] = 0;
	fi(2, n) {
		if (a[i] > a[i - 1]) {
			t[a[i]] = 0;
			continue;
		}
		dbg(t);
		while (sz(t)) {
			int x = (*t.rbegin()).first;
			if (x > a[i]) {				
				t.erase(x);				
			} else {
				break;
			}
		}
		
		int x = a[i];
		int add = 1;
		while (add && x >= 0) {
			int val = t[x] + 1;
			add = val / S;
			val %= S;
			t[x] = val;					
			x--;
		}
		if (t.count(0)) break;
	}
	if (t.count(0)) return false;
	return true;
}

void solve() {
	bool one = true;
	fi(2, n) {
		if (a[i] <= a[i - 1]) one = false;
	}
	if (one) {
		printf("1\n");
		return;
	}
	int l = 1;
	int r = INF;
	while (r - l > 1) {
		int h = (l + r) / 2;
		if (can(h)) {
			r = h;
		} else {
			l = h;
		}
	}
	printf("%d\n", r);
}

int main() {
#ifdef LOCAL
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
	START_TIME = (double)clock();
#endif

  scanf("%d", &n);
  fi(1, n) {
  	scanf("%d", &a[i]);
  }
	solve();

	exit();
	return 0;
}





Measured memory_bytes: 3840