// https://atcoder.jp/contests/agc029/tasks/agc029_c
//
#![allow(unused_imports)]
use std::io::*;
use std::io::Write;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;

// Input macros.
// Original by tanakh: https://qiita.com/tanakh/items/0ba42c7ca36cd29d0ac8
#[allow(unused_macros)]
macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    ($($r:tt)*) => {
        let s = {
            use std::io::Read;
            let mut s = String::new();
            std::io::stdin().read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! input_inner {
    ($iter:expr) => {};
    ($iter:expr, ) => {};

    ($iter:expr, $var:ident : $t:tt $($r:tt)*) => {
        let $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };

    ($iter:expr, mut $var:ident : $t:tt $($r:tt)*) => {
        let mut $var = read_value!($iter, $t);
        input_inner!{$iter $($r)*}
    };
}

#[allow(unused_macros)]
macro_rules! read_value {
    ($iter:expr, ( $($t:tt),* )) => {
        ( $(read_value!($iter, $t)),* )
    };

    ($iter:expr, [ $t:tt ; $len:expr ]) => {
        (0..$len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
    };

    ($iter:expr, [ next / $t:tt ]) => {
        {
            let len = read_value!($iter, usize);
            (0..len).map(|_| read_value!($iter, $t)).collect::<Vec<_>>()
        }
    };

    ($iter:expr, switch) => {
        {
            let ty = read_value!($iter, i32);
            if ty == 1 {
                vec![ty, read_value!($iter, i32), read_value!($iter, i32)]
            } else if ty == 2 {
                vec![ty, read_value!($iter, i32)]
            } else {
                vec![ty, read_value!($iter, i32)]
            }
        }
    };

    ($iter:expr, chars) => {
        read_value!($iter, String).chars().collect::<Vec<char>>()
    };

    ($iter:expr, usize1) => {
        read_value!($iter, usize) - 1
    };

    ($iter:expr, $t:ty) => {
        $iter.next().unwrap().parse::<$t>().expect("Parse error")
    };
}

#[allow(unused_macros)]
macro_rules! read_line {
    ($t:tt) => {
        {
            let mut s = String::new();
            std::io::stdin().read_line(&mut s).unwrap();
            s.trim_right().parse::<$t>().unwrap()
        }
    }
}

#[allow(unused_macros)]
macro_rules! dvec {
    ($t:expr ; $len:expr) => {
        vec![$t; $len]
    };

    ($t:expr ; $len:expr, $($rest:expr),*) => {
        vec![dvec!($t; $($rest),*); $len]
    };
}

#[allow(unused_macros)]
macro_rules! ifv {
    ($t:expr, $a:expr, $b: expr) => {
        if $t { $a } else { $b }
    }
}

#[allow(unused_macros)]
macro_rules! fill {
    ($t:expr, $v:expr) => {
        for i in 0..$t.len() {
            $t[i] = $v;
        }
    };
}

#[allow(unused_macros)]
macro_rules! join {
    ($t:expr, $glue:expr) => {
        $t.into_iter().map(|w| w.to_string()).collect::<Vec<_>>().join($glue)
    };
}

#[allow(unused_macros)]
macro_rules! debug {
    ($($a:expr),*) => {
        println!(concat!($(stringify!($a), " = {:?}, "),*), $($a),*);
    }
}

// ===

type Stack = VecDeque<(usize, i64)>;

fn increment(limit: usize, mut stack: Stack) -> Option<Stack> {
    let mut zeros = 0;
    while stack.len() >= 1 {
        let (c, num) = stack.pop_back().unwrap();
        if c == limit-1 {
            zeros += num;
        } else {
            if num >= 2 {
                stack.push_back((c, num-1));
            }
            stack.push_back((c+1, 1));
            if zeros >= 1 {
                stack.push_back((0, zeros));
            }
            return Some(stack);
        }
    }
    return None;
}

fn is_possible(limit: usize, a: &Vec<i64>) -> bool {
    let mut stack = VecDeque::new();
    let mut all = 0;
    let n = a.len();
    for i in 0..n {
        if all < a[i] {
            stack.push_back((0, a[i]-all));
            all = a[i];
        } else {
            while all > a[i] {
                let (c, num) = stack.pop_back().unwrap();
                if all-num >= a[i] {
                    all -= num;
                } else {
                    let want = a[i]-(all-num);
                    stack.push_back((c, want));
                    all = a[i];
                    break;
                }
            }
            if let Some(incs) = increment(limit, stack) {
                stack = incs;
            } else {
                return false;
            }
        }
        all = a[i];
    }
    true
}

fn main() {
    input! {
        n: usize,
        a: [i64; n]
    };

    let mut ng = 0;
    let mut ok = n;

    while ok - ng > 1 {
        let med = (ok + ng) / 2;
        if is_possible(med, &a) {
            ok = med;
        } else {
            ng = med;
        }
    }
    println!("{}", ok);
}


Measured memory_bytes: 13932