#![allow(unused_imports, unused_macros)]

use kyoproio::*;
use std::{
    collections::*,
    io::{self, prelude::*},
    iter,
    mem::{replace, swap},
};

fn run<I: Input, O: Write>(mut kin: I, mut out: O) {
    macro_rules! output { ($($args:expr),+) => { write!(&mut out, $($args),+).unwrap(); }; }
    macro_rules! outputln {
        ($($args:expr),+) => { output!($($args),+); outputln!(); };
        () => { output!("\n"); if cfg!(debug_assertions) { out.flush().unwrap(); } }
    }

    let n: usize = kin.input();
    let mut a: Vec<i32> = kin.seq(n);
    a.sort();
    let mut b = Vec::new();
    for a in a {
        if let Some((x, l)) = b.last_mut() {
            if *x == a {
                *l += 1;
            } else {
                b.push((a, 1));
            }
        } else {
            b.push((a, 1));
        }
    }
    let mut ans = 0;
    let mut c = Vec::new();
    while !b.is_empty() {
        c.clear();
        ans += 1;
        let mut prev = -10;
        for &(x, l) in b.iter() {
            if prev + 1 >= x {
                c.push((x, l));
            } else {
                if l > 1 {
                    c.push((x, l - 1));
                }
                prev = x;
            }
        }
        swap(&mut b, &mut c);
    }
    outputln!("{}", ans);
}

// -----------------------------------------------------------------------------
fn main() -> io::Result<()> {
    std::thread::Builder::new()
        .stack_size(64 * 1024 * 1024)
        .spawn(|| {
            run(
                KInput::new(io::stdin().lock()),
                io::BufWriter::new(io::stdout().lock()),
            )
        })?
        .join()
        .unwrap();
    Ok(())
}

// -----------------------------------------------------------------------------
pub mod kyoproio {
    use std::{io::prelude::*, mem};
    pub trait Input {
        fn bytes(&mut self) -> &[u8];
        fn str(&mut self) -> &str {
            std::str::from_utf8(self.bytes()).unwrap()
        }
        fn input<T: InputParse>(&mut self) -> T {
            T::input(self)
        }
        fn iter<T: InputParse>(&mut self) -> Iter<T, Self> {
            Iter(self, std::marker::PhantomData)
        }
        fn seq<T: InputParse, B: std::iter::FromIterator<T>>(&mut self, n: usize) -> B {
            self.iter().take(n).collect()
        }
    }
    pub struct KInput<R> {
        src: R,
        buf: Vec<u8>,
        pos: usize,
        len: usize,
    }
    impl<R: Read> KInput<R> {
        pub fn new(src: R) -> Self {
            Self {
                src,
                buf: vec![0; 1 << 16],
                pos: 0,
                len: 0,
            }
        }
    }
    impl<R: Read> Input for KInput<R> {
        fn bytes(&mut self) -> &[u8] {
            loop {
                while let Some(delim) = self.buf[self.pos..self.len]
                    .iter()
                    .position(|b| b.is_ascii_whitespace())
                {
                    let p = self.pos;
                    self.pos += delim + 1;
                    if delim > 0 {
                        return &self.buf[p..p + delim];
                    }
                }
                if self.pos > 0 {
                    self.buf.copy_within(self.pos..self.len, 0);
                    self.len -= self.pos;
                    self.pos = 0;
                }
                if self.len >= self.buf.len() {
                    self.buf.resize(2 * self.buf.len(), 0);
                }
                let read = self.src.read(&mut self.buf[self.len..]).unwrap();
                if read == 0 {
                    return &self.buf[mem::replace(&mut self.pos, self.len)..self.len];
                }
                self.len += read;
            }
        }
    }
    pub struct Iter<'a, T, I: ?Sized>(&'a mut I, std::marker::PhantomData<*const T>);
    impl<'a, T: InputParse, I: Input + ?Sized> Iterator for Iter<'a, T, I> {
        type Item = T;
        fn next(&mut self) -> Option<T> {
            Some(self.0.input())
        }
        fn size_hint(&self) -> (usize, Option<usize>) {
            (!0, None)
        }
    }
    pub trait InputParse: Sized {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self;
    }
    impl InputParse for Vec<u8> {
        fn input<I: Input + ?Sized>(src: &mut I) -> Self {
            src.bytes().to_owned()
        }
    }
    macro_rules! from_str_impl {
        { $($T:ty)* } => {
            $(impl InputParse for $T {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    src.str().parse::<$T>().unwrap()
                }
            })*
        }
    }
    from_str_impl! { String char bool f32 f64 }
    macro_rules! parse_int_impl {
        { $($I:ty: $U:ty)* } => {
            $(impl InputParse for $I {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    let f = |s: &[u8]| s.iter().fold(0, |x, b| 10 * x + (b & 0xf) as $I);
                    let s = src.bytes();
                    if let Some((&b'-', t)) = s.split_first() { -f(t) } else { f(s) }
                }
            }
            impl InputParse for $U {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    src.bytes().iter().fold(0, |x, b| 10 * x + (b & 0xf) as $U)
                }
            })*
        };
    }
    parse_int_impl! { isize:usize i8:u8 i16:u16 i32:u32 i64:u64 i128:u128 }
    macro_rules! tuple_impl {
        ($H:ident $($T:ident)*) => {
            impl<$H: InputParse, $($T: InputParse),*> InputParse for ($H, $($T),*) {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    ($H::input(src), $($T::input(src)),*)
                }
            }
            tuple_impl!($($T)*);
        };
        () => {}
    }
    tuple_impl!(A B C D E F G);
    macro_rules! array_impl {
        { $($N:literal)* } => {
            $(impl<T: InputParse> InputParse for [T; $N] {
                fn input<I: Input + ?Sized>(src: &mut I) -> Self {
                    let mut arr = mem::MaybeUninit::uninit();
                    unsafe {
                        let ptr = arr.as_mut_ptr() as *mut T;
                        for i in 0..$N {
                            ptr.add(i).write(src.input());
                        }
                        arr.assume_init()
                    }
                }
            })*
        };
    }
    array_impl! { 1 2 3 4 5 6 7 8 }
    #[macro_export]
    macro_rules! kdbg {
        ($($v:expr),*) => {
            if cfg!(debug_assertions) { dbg!($($v),*) } else { ($($v),*) }
        }
    }
}