#![allow(unused_imports)]
#![allow(non_snake_case)]
use std::cmp::*;
use std::collections::*;
use std::io::Write;

#[allow(unused_macros)]
macro_rules! debug {
    ($($e:expr),*) => {
        #[cfg(debug_assertions)]
        $({
            let (e, mut err) = (stringify!($e), std::io::stderr());
            writeln!(err, "{} = {:?}", e, $e).unwrap()
        })*
    };
}

fn main() {
    let n = read::<usize>();
    let a = read_vec::<usize>();
    let mut unique = vec![1];
    for i in 1..n {
        if a[i] == a[i - 1] {
            let last = unique.len() - 1;
            unique[last] += 1;
        } else {
            unique.push(1);
        }
    }
    if unique.len() == 1 {
        println!("{}", unique.len());
        return;
    }

    let mut dp = vec![0; unique.len() + 1];
    dp[0] = 0;
    dp[1] = unique[0];
    dp[2] = unique[1];

    for i in 2..unique.len() {
        dp[i + 1] = unique[i] + max(dp[i - 1], dp[i - 2]);
    }
    println!("{}", max(dp[dp.len() - 1], dp[dp.len() - 2]));
}

fn read<T: std::str::FromStr>() -> T {
    let mut s = String::new();
    std::io::stdin().read_line(&mut s).ok();
    s.trim().parse().ok().unwrap()
}

fn read_vec<T: std::str::FromStr>() -> Vec<T> {
    read::<String>()
        .split_whitespace()
        .map(|e| e.parse().ok().unwrap())
        .collect()
}