use std::cmp::Reverse;

use proconio::input;

fn main() {
    input! {
        (n, m): (usize, usize),
        cd: [(usize, usize); n],
    }

    let mut costless_damage = 0_usize;
    let mut cards = vec![];
    for &(c, d) in &cd {
        if c == 0 {
            costless_damage += d;
        } else {
            cards.push(Card { cost: c, damage: d });
        }
    }

    cards.sort_unstable_by_key(|card| Reverse(card.cost));

    let mut dp = vec![None::<usize>; m + 1];
    dp[m] = Some(costless_damage);
    for &card in &cards {
        for prev_sum_cost in card.cost..=m {
            if let Some(prev_sum_damage) = dp[prev_sum_cost] {
                chmax_for_option(
                    &mut dp[(prev_sum_cost - card.cost) / 2],
                    prev_sum_damage + card.damage,
                );
            }
        }
    }

    let max_sum_damage = dp
        .iter()
        .filter_map(|&sum_damage| sum_damage)
        .max()
        .unwrap();
    println!("{}", max_sum_damage);
}

#[derive(Debug, Clone, Copy)]
struct Card {
    cost: usize,
    damage: usize,
}

/// If `value` is `None` or contains a value less than `cand_value`, update it to `Some(cand_value)`.
///
/// Returns whether `value` has been updated or not as a bool value.
///
/// # Arguments
///
/// * `value` - Reference variable to be updated.
/// * `cand_value` - Candidate value for update.
pub fn chmax_for_option<T>(value: &mut Option<T>, cand_value: T) -> bool
where
    T: PartialOrd,
{
    if value.as_ref().is_some_and(|cost| cost >= &cand_value) {
        return false;
    }

    *value = Some(cand_value);

    true
}