use std::{cmp::Reverse, collections::BTreeMap};

use proconio::input;

const MAX_NUM_CARDS: usize = 23;

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 add_damage = if m <= 1000 {
        strategy1(&cards, m)
    } else {
        strategy2(&cards, m)
    };
    println!("{}", costless_damage + add_damage);
}

fn strategy1(cards: &[Card], m: usize) -> usize {
    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] {
                    chmax_for_option(
                        &mut next_dp[num_card][sum_cost],
                        prev_sum_damage + card.damage,
                    );
                }
            }
        }

        dp = next_dp;
    }

    dp.iter()
        .flatten()
        .filter_map(|&damage| damage)
        .max()
        .unwrap()
}

fn strategy2(cards: &[Card], m: usize) -> usize {
    let mut dp = vec![BTreeMap::<usize, usize>::new(); MAX_NUM_CARDS + 1];
    dp[0].insert(0, 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 (&prev_sum_cost, &prev_sum_damage) in
                dp[num_card - 1].range(..(m + 1).saturating_sub(raised_cost))
            {
                let sum_cost = prev_sum_cost + raised_cost;
                let cand_sum_damage = prev_sum_damage + card.damage;
                let sum_damage = next_dp[num_card].entry(sum_cost).or_default();
                *sum_damage = (*sum_damage).max(cand_sum_damage);
            }
        }

        dp = next_dp;
    }

    *dp.iter()
        .map(|sub_dp| sub_dp.values())
        .flatten()
        .max()
        .unwrap()
}

#[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
}