use std::cmp::Reverse;

use proconio::input;

// コストが正のカードは高々9枚しか使用できない
const MAX_NUM_CARDS: usize = 9;

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

    let mut cards = cd
        .iter()
        .map(|&(c, d)| Card { cost: c, damage: d })
        .collect::<Vec<_>>();

    let costless_damage = cards
        .iter()
        .filter_map(|card| {
            if card.cost == 0 {
                Some(card.damage)
            } else {
                None
            }
        })
        .sum::<usize>();

    cards.retain(|card| card.cost != 0);
    cards.sort_unstable_by_key(|card| Reverse(card.cost));

    // dp[i][j]: i枚使用してコストの合計がjのときの合計ダメージ
    let mut dp = vec![vec![None::<usize>; m + 1]; MAX_NUM_CARDS + 1];
    dp[0][0] = Some(0);
    for &card in &cards {
        let mut next_dp = dp.clone();

        for num_card in 1..=MAX_NUM_CARDS {
            let raised_cost = card.cost << (num_card - 1);
            for sum_cost in raised_cost..=m {
                if let Some(prev_sum_damage) = dp[num_card - 1][sum_cost - raised_cost] {
                    chmin_for_option(
                        &mut next_dp[num_card][sum_cost],
                        prev_sum_damage + card.damage,
                    );
                }
            }
        }

        dp = next_dp;
    }

    let add_damage = dp
        .iter()
        .flatten()
        .filter_map(|&damage| damage)
        .max()
        .unwrap();
    println!("{}", costless_damage + add_damage);
}

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

/// If `value` is `None` or contains a value greater 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 chmin_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
}