#define STOPIT
#include <bits/stdc++.h>
#define loop(n) for (lint ngtkana_is_a_genius = 0; ngtkana_is_a_genius < lint(n); ngtkana_is_a_genius++)
#define rep(i, begin, end) for (lint i = lint(begin); (i) < lint(end); i++)
#define all(v) v.begin(), v.end()
#define rand(l, r) std::uniform_int_distribution<>(l, r)(mt)
using lint = long long;
auto mt = std::mt19937_64(std::random_device{}());
auto cmn = [](auto& a, auto b){ if (a > b) {a = b; return true;} return false; };
auto cmx = [](auto& a, auto b){ if (a < b) {a = b; return true;} return false; };
void debug_impl() { std::cerr << std::endl; }
template <typename Head, typename... Tail>
void debug_impl(Head head, Tail... tail) { std::cerr << " " << head; debug_impl(tail...); }
#ifndef STOPIT
#define debug(...)\
  do {\
    std::cerr << std::boolalpha << "[" << #__VA_ARGS__ << "]:";\
    debug_impl(__VA_ARGS__);\
    std::cerr << std::noboolalpha;\
  } while (false)
#else
#define debug(...) {}
#endif

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr>
std::istream& operator>> (std::istream& is, Container& v)
  { for (auto & x : v) { is >> x; } return is; }

template < typename Container, typename Value = typename Container::value_type, std::enable_if_t<!std::is_same< Container, std::string >::value, std::nullptr_t> = nullptr >
std::ostream& operator<< (std::ostream& os, Container const& v) {
 os << "{";
  for (auto it = v.begin(); it != v.end(); it++)
    {os << (it != v.begin() ? "," : "") << *it;}
  return os << "}";
}

template < template < typename ... > class Tuple,  typename... Args, std::size_t ... Inds, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::istream& tuple_input_impl(std::istream& os, Tuple<Args...>& tuple, std::integer_sequence<std::size_t, Inds...>)
  { (void)std::initializer_list<int>{((void)(os >> std::get< Inds >(tuple)), 0)...}; return os; }
template < template < typename ... > class Tuple,  typename... Args, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::istream& operator>> (std::istream& os, Tuple<Args...>& tuple)
  { return tuple_input_impl(os, tuple, std::index_sequence_for<Args...>()); }

template < template < typename ... > class Tuple,  typename... Args, std::size_t ... Inds, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::ostream& tuple_output_impl(std::ostream& os, const Tuple<Args...>& tuple, std::integer_sequence<std::size_t, Inds...>)
  { os << "("; (void)std::initializer_list<int>{((void)(os << (Inds > 0 ? "," : "") << std::get< Inds >(tuple)), 0)...}; return os << ")"; }
template < template < typename ... > class Tuple,  typename... Args, std::size_t = std::tuple_size< Tuple < Args ... > >::value >
std::ostream& operator<< (std::ostream& os, const Tuple<Args...>& tuple)
 { return tuple_output_impl(os, tuple, std::index_sequence_for<Args...>()); }

template < class Value >
bool bat(Value x, std::size_t pos) { return (x >> pos) & Value{1}; }

/*
半分全列挙です。
前半と後半に分けて、あり得る組み合わせをすべて調べて、重さと価値のペアにしておきます。
さらに、重さの lower_bound を使いたいので、価値が単調増加になるように。価値のないものは一個前と同じ価値まで引き上げます。
前半を全探索して、後半をギリギリまで詰め込めばよいです。
*/

int main() {
  std::cin.tie(0); std::cin.sync_with_stdio(false);
  int n; lint W; std::cin >> n >> W;
  int l = n / 2, m = n - l;
  debug(l,m,n);
  std::vector<std::pair<lint,lint>> data(n); std::cin>>data;
  debug(data);

  auto make_combis = [&] (auto&& pairs) {
    int n = pairs.size();
    int N = 1 << n;
    std::vector<std::pair<lint,lint>> ans(N);
    rep(bs,0,N) {
      lint v = 0, w = 0;
      rep(i,0,n) {
        if (bat(bs,i)) {
          v += pairs.at(i).first;
          w += pairs.at(i).second;
        }
      }
      ans.at(bs) = std::make_pair(w,v);
    }

    std::sort(all(ans));
    rep(i,1,N) {
      auto&& prv = ans.at(i-1);
      auto&& crr = ans.at(i);
      cmx(crr.second, prv.second);
    }
    return ans;
  };
  auto former = make_combis(std::vector<std::pair<lint,lint>>(data.begin(), data.begin() + l));
  auto latter = make_combis(std::vector<std::pair<lint,lint>>(data.begin() + l, data.end()));
  debug(former, latter);

  lint ans = 0;
  lint inf = std::numeric_limits<lint>::max();
  for (auto&& pair : former) {
    lint w0,v0; std::tie(w0,v0) = pair;
    auto it = std::upper_bound(all(latter), std::make_pair(W - w0,inf));
    if (it == latter.begin()) continue;
    it--;
    lint w1,v1; std::tie(w1,v1) = *it;
    debug(pair,*it);
    assert(w0 + w1 <= W);
    lint tmp = v0 + v1;
    cmx(ans, tmp);
  }
  std::cout << ans << std::endl;
  return 0;
}


Measured memory_bytes: 35640