#include<bits/stdc++.h>
using namespace std;
#define REP(i,m,n) for(int i=(int)m ; i < (int) n ; ++i )
#define rep(i,n) REP(i,0,n)

int main(){
    int n;cin>>n;
    int a[n];
    rep(i,n)cin>>a[i];
    bool inc=true;
    rep(i,n-1)if(a[i]>=a[i+1])inc=false;
    if(inc){
        cout<<1<<endl;
        return 0;
    }
    int ng=1,ok=n;
    while(ok-ng>1){
        int mid=(ok+ng)/2;
        vector<pair<int,int>> v;
        v.emplace_back(-1,-1);
        bool can=true;
        rep(i,n-1){
            if(a[i]<a[i+1])continue;
            int m=a[i+1];
            while(v.back().first>m)v.pop_back();
            while(v.back().first==m&&v.back().second==mid-1)v.pop_back(),--m;
            if(m==v.back().first)++v.back().second;
            else if(m)v.emplace_back(m,1);
            else {
                can=false;
                break;
            }
        }
        if(can)ok=mid;
        else ng=mid;
    }
    cout<<ok<<endl;
    return 0;
}
