// Macro by MasuqaT (occar421)
// https://github.com/occar421/ProgrammingContest/tree/master/templates/src/standard_io.rs

use std::cmp::max;
use std::io;
use std::io::{BufRead, Write};
use std::ops::{Div, Mul, Rem};

macro_rules! input {
    (source = $s:expr, $($r:tt)*) => {
        let mut iter = $s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
    (stdin = $s:expr, $($r:tt)*) => {
        let s = {
            let mut s = String::new();
            $s.read_to_string(&mut s).unwrap();
            s
        };
        let mut iter = s.split_whitespace();
        input_inner!{iter, $($r)*}
    };
}

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)*}
    };
}

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<_>>()
    };

    ($iter:expr, chars) => {
        read_value!($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! assert_judge {
    ($method:ident, $input:expr, $expected:expr) => {{
        let input = $input.as_bytes();
        let mut output = Vec::new();

        $method(&input[..], &mut output);

        let output = String::from_utf8(output).expect("Not UTF-8");

        assert_eq!($expected, output);
    }};
}

#[allow(unused_macros)]
macro_rules! assert_judge_with_output {
    ($method:ident, $input:expr) => {{
        let input = $input.as_bytes();
        let mut output = Vec::new();

        $method(&input[..], &mut output);

        String::from_utf8(output).expect("Not UTF-8")
    }};
}

#[allow(unused_macros)]
macro_rules! assert_eq_with_error {
    ($left:expr, $right:expr, $precision:expr) => {{
        match (&$left, &$right, &$precision) {
            (left_val, right_val, precision_val) => {
                if !(*left_val - *precision_val < *right_val
                    && *right_val < *left_val + *precision_val)
                {
                    // The reborrows below are intentional. Without them, the stack slot for the
                    // borrow is initialized even before the values are compared, leading to a
                    // noticeable slow down.
                    panic!(
                        r#"assertion failed: `(left == right) +- precision`
      left: `{:?}`,
     right: `{:?}`,
 precision: `{:?}`"#,
                        &*left_val, &*right_val, &*precision_val
                    )
                }
            }
        }
    }};
}

trait GenericInteger:
Copy + PartialEq + Rem<Output=Self> + Div<Output=Self> + Mul<Output=Self>
{
    fn zero() -> Self;
}

macro_rules! dec_gi {
    () => {};
    ($t:ty $(, $r:ty)*) => {
        impl GenericInteger for $t {
            #[inline]
            fn zero() -> Self { 0 }
        }

        dec_gi![ $( $r ),* ];
    };
}

dec_gi![u8, u16, u32, u64, u128, usize, i8, i16, i32, i64, i128, isize];

#[allow(dead_code)]
fn gcd<T>(a: T, b: T) -> T
    where
        T: GenericInteger,
{
    if b == T::zero() {
        a
    } else {
        gcd(b, a % b)
    }
}

#[allow(dead_code)]
fn lcm<T>(a: T, b: T) -> T
    where
        T: GenericInteger,
{
    a / gcd(a, b) * b
}

#[allow(unused_macros)]
macro_rules! swap {
    ($v1:expr, $v2:expr) => {
        let buf = $v1;
        $v1 = $v2;
        $v2 = buf;
    };
}

fn main() {
    let stdio = io::stdin();
    let input = stdio.lock();

    let output = io::stdout();

    process(input, output);
}

fn process<R, W>(mut reader: R, mut writer: W) -> ()
    where
        R: BufRead,
        W: Write,
{
    input! {
        stdin = reader,
        n: usize,
        v: [u16; n]
    }

    if n == 1 {
        write!(writer, "{}", v[0]);
        return;
    }
    if n == 2 {
        write!(writer, "{}", max(v[0], v[1]));
        return;
    }

    let v: Vec<u16> = v;
    let mut dp = vec![0; n];
    dp[0] = v[0];
    dp[1] = v[1];
    dp[2] = v[0] + v[2];
    for (index, value) in v.iter().enumerate().skip(3) {
        dp[index] = value + max(dp[index - 3], dp[index - 2]);
    }

    write!(writer, "{}", max(dp[n - 2], dp[n - 1]));
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn sample1() {
        assert_judge!(
            process,
"
4
1 2 3 4
", "6");
    }

    #[test]
    fn sample2() {
        assert_judge!(
            process,
"
4
5 4 4 9
", "14");
    }

    #[test]
    fn sample3() {
        assert_judge!(
            process,
"
7
1 2 9 10 1 1 4
", "16");
    }

    #[test]
    fn sample4() {
        assert_judge!(
            process,
"
1
100
", "100");
    }
}