#[macro_export]
macro_rules! setup {
    { mut $input:ident: SplitWhitespace $(,)? } => {
        use std::io::Read;
        let mut buf = String::new();
        std::io::stdin().read_to_string(&mut buf).unwrap();
        let mut $input = buf.split_whitespace();
    };
}

#[macro_export]
macro_rules! parse_next {
    ($str_iter:expr) => {
        $str_iter.next().unwrap().parse().unwrap()
    };
}

fn main() {
    setup! { mut input: SplitWhitespace };

    let n: usize = parse_next!(input);
    let mut a: Vec<usize> = (0..n).map(|_| parse_next!(input)).collect();

    a.sort();

    let mut count = 0;
    while !a.is_empty() {
        let mut idxs = vec![0];
        let mut size = a[0];
        for i in 1..a.len() {
            if size + 1 < a[i] {
                idxs.push(i);
                size = a[i];
            }
        }
        idxs.reverse();
        for idx in idxs.into_iter() {
            a.remove(idx);
        }
        count += 1;
    }

    println!("{}", count);
}