#include <bits/stdc++.h>
using namespace std;
#if __has_include(<boost/multiprecision/cpp_int.hpp>)
	#include <boost/multiprecision/cpp_int.hpp>
	#include <boost/multiprecision/cpp_dec_float.hpp>
	using bll = boost::multiprecision::cpp_int;
	using bdouble = boost::multiprecision::cpp_dec_float_100;
	using namespace boost::multiprecision;
#endif
#if __has_include(<boost/stacktrace.hpp>)
	#define BOOST_STACKTRACE_USE_ADDR2LINE
	#define BOOST_STACKTRACE_ADDR2LINE_LOCATION /usr/local/opt/binutils/bin/addr2line
	#define _GNU_SOURCE 1
	#include <boost/stacktrace.hpp>
#endif
#ifdef LOCAL_TEST
	namespace std {
		template<typename T> class dvector : public std::vector<T> {
		public:
			dvector() : std::vector<T>() {}
			explicit dvector(size_t n, const T& value = T()) : std::vector<T>(n, value) {}
			dvector(const std::vector<T>& v) : std::vector<T>(v) {}
			dvector(const std::initializer_list<T> il) : std::vector<T>(il) {}
			dvector(const std::string::iterator first, const std::string::iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::iterator first, const typename std::vector<T>::iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::reverse_iterator first, const typename std::vector<T>::reverse_iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::const_iterator first, const typename std::vector<T>::const_iterator last) : std::vector<T>(first, last) {}
			dvector(const typename std::vector<T>::const_reverse_iterator first, const typename std::vector<T>::const_reverse_iterator last) : std::vector<T>(first, last) {}
			T& operator[](size_t n) {
				try { return this->at(n); } catch (const std::exception& e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; return this->at(n); }
			}
			const T& operator[](size_t n) const {
				try { return this->at(n); } catch (const std::exception& e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; return this->at(n); }
			}
		};
	}
	class dbool {
	private:
		bool boolvalue;
	public:
		dbool() : boolvalue(false) {}
		dbool(bool b) : boolvalue(b) {}
		operator bool&() { return boolvalue; }
		operator const bool&() const { return boolvalue; }
	};
	#define vector dvector
	#define bool dbool
#endif
#ifdef LOCAL_DEV
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<T>& v) {
		for (size_t i = 0; i < v.size(); ++i){ s << v[i]; if (i < v.size() - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::vector<std::vector<T>>& vv) {
		s << "\\\n"; for (size_t i = 0; i < vv.size(); ++i){ s << vv[i] << "\n"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::deque<T>& v) {
		for (size_t i = 0; i < v.size(); ++i){ s << v[i]; if (i < v.size() - 1) s << "\t"; } return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::set<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template<typename T> std::ostream& operator<<(std::ostream& s, const std::multiset<T>& se) {
		s << "{ "; for (auto itr = se.begin(); itr != se.end(); ++itr){ s << (*itr) << "\t"; } s << "}"; return s; }
	template <typename T, size_t N> std::ostream& operator<<(std::ostream& s, const std::array<T, N>& a) {
		s << "{ "; for (size_t i = 0; i < N; ++i){ s << a[i] << "\t"; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::map<T1, T2>& m) {
		s << "{\n"; for (auto itr = m.begin(); itr != m.end(); ++itr){ s << "\t" << (*itr).first << " : " << (*itr).second << "\n"; } s << "}"; return s; }
	template<typename T1, typename T2> std::ostream& operator<<(std::ostream& s, const std::pair<T1, T2>& p) {
		return s << "(" << p.first << ", " << p.second << ")"; }
	class SIGFPE_exception : std::exception {};
	class SIGSEGV_exception : std::exception {};
	void catch_SIGFPE([[maybe_unused]] int e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; throw SIGFPE_exception(); }
	void catch_SIGSEGV([[maybe_unused]] int e) { std::cerr << boost::stacktrace::stacktrace() << '\n'; throw SIGSEGV_exception(); }
	signed convertedmain();
	signed main() { signal(SIGFPE, catch_SIGFPE); signal(SIGSEGV, catch_SIGSEGV); return convertedmain(); }
	#define main() convertedmain()
	void debug_impl() { std::cerr << '\n'; }
	template<typename Head, typename... Tail> void debug_impl(Head head, Tail... tail) { std::cerr << " " << head << (sizeof...(tail) ? "," : ""); debug_impl(tail...); }
	#define debug(...) do { std::cerr << "(" << #__VA_ARGS__ << ") ="; debug_impl(__VA_ARGS__); } while (false)
#else
	#define debug(...) do {} while (false)
#endif
//#define int long long
using ll = long long;
//constexpr int INF = (ll)1e9 + 7;//INT_MAX=(1<<31)-1=2147483647
constexpr ll INF = (ll)1e18;//(1LL<<63)-1=9223372036854775807
constexpr ll MOD = (ll)1e9 + 7;
constexpr double EPS = 1e-9;
constexpr ll dx[4] = {1, 0, -1, 0};
constexpr ll dy[4] = {0, 1, 0, -1};
constexpr ll dx8[8] = {1, 0, -1, 0, 1, 1, -1, -1};
constexpr ll dy8[8] = {0, 1, 0, -1, 1, -1, 1, -1};
#define rep(i, n)   for(ll i=0, i##_length=(n); i< i##_length; ++i)
#define repeq(i, n) for(ll i=1, i##_length=(n); i<=i##_length; ++i)
#define rrep(i, n)   for(ll i=(n)-1; i>=0; --i)
#define rrepeq(i, n) for(ll i=(n)  ; i>=1; --i)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
void p() { std::cout << '\n'; }
template<typename Head, typename... Tail> void p(Head head, Tail... tail) { std::cout << head << (sizeof...(tail) ? " " : ""); p(tail...); }
template<typename T> inline void pv(std::vector<T>& v) { for(ll i=0, N=v.size(); i<N; i++) std::cout << v[i] << " \n"[i==N-1]; }
template<typename T> inline bool chmax(T& a, T b) { return a < b && (a = b, true); }
template<typename T> inline bool chmin(T& a, T b) { return a > b && (a = b, true); }
template<typename T> inline void uniq(std::vector<T>& v) { v.erase(std::unique(v.begin(), v.end()), v.end()); }

/*-----8<-----template-----8<-----*/

class Item{
public:
	ll value, weight, index;
	Item() {}
	Item(ll value, ll weight, ll index) : value(value), weight(weight), index(index) {}
};
ostream& operator<<(ostream& s, const Item& item) {
	s << "{ " << item.index << " : value = " << item.value << ", weight = " << item.weight << " }";
	return s;
}

class KnapsackBB{
public:
	vector<Item> items;
	ll N;
	ll W;
	//現在探索している商品の選び方　used_items[i]=true -> i番目の商品を選択
	vector<bool> used_items;
	//現時点で最適な商品の選び方　opt_items[i]=true -> i番目の商品を選択
	vector<bool> opt_items;
	//現時点で最適な商品の選び方をしたときの価値合計
	ll opt_value=0;

	KnapsackBB(vector<Item> &items, ll W) : items(items), N(items.size()), W(W) {}

	//分枝限定法で探索
	//index=index-1番目の商品までは選択が終わった、index番目からの商品はまだ調べてない
	//value=今のところの価値合計
	//weight=今のところの重さ合計
	void solvebb(ll index, ll value, ll weight){
		//全部調べ終わった
		if(index==N || items[index].value<=0){
			if(opt_value < value){
				opt_items=used_items;
				opt_value=value;
			}
			return;
		}

		//緩和問題を解く
		ll tmp_weight=weight;
		double tmp_value=value;
		for(ll i=index; i<N; i++){
			if(tmp_weight+items[i].weight == W){
				//緩和問題の解が元の問題でも実現可能→暫定解として使えるかも
				tmp_value+=items[i].value;
				if(opt_value<tmp_value){
					opt_value=tmp_value;
					opt_items=used_items;
					for(ll j=index; j<=i; j++){
						opt_items[j]=true;
					}
				}
				return;
			}else if(tmp_weight+items[i].weight < W){
				tmp_value+=items[i].value;
				tmp_weight+=items[i].weight;
			}else{
				//重さの余りを詰める
				tmp_value+=(double)items[i].value*(W-tmp_weight)/items[i].weight;
				tmp_weight=W;
				break;
			}
		}

		//緩和問題ですら暫定解を超えられない→これ以上調査する意味がない
		if(tmp_value < opt_value){
			return;
		}

		//重量制限が許されれば、index番目を選ぶ場合で探索
		if(weight+items[index].weight <= W){
			used_items[index]=true;
			solvebb(index+1, value+items[index].value, weight+items[index].weight);
		}
		//index番目を選ばない場合で探索
		used_items[index]=false;
		solvebb(index+1, value, weight);
	}

	ll solve(){
		//商品をコスパのよい順に並び替え
		sort(items.begin(), items.end(), [](const Item &x, const Item &y) {
			return ((double)x.value/x.weight) > ((double)y.value/y.weight);
		});

		//暫定解として貪欲に選んでみる
		ll tmp_weight=0,tmp_value=0;
		vector<bool> tmp_items(N,false);
		for(ll i=0; i<N; i++){
			if(items[i].value<=0)break;
			if(tmp_weight+items[i].weight <= W){
				tmp_value+=items[i].value;
				tmp_weight+=items[i].weight;
				tmp_items[i]=true;
			}
		}
		opt_items=tmp_items;
		opt_value=tmp_value;
		used_items.assign(N,false);
		solvebb(0,0,0);
		return opt_value;
	}
};

/*-----8<-----library-----8<-----*/

signed main() {
	//Nが大きいとTLEするので注意！！
	//N=3000でTLE実績あり(https://atcoder.jp/contests/abc145/submissions/8480788)

	//ABC032D
	//https://atcoder.jp/contests/abc032/tasks/abc032_d
	ll N,W;
	cin >> N >> W;
	vector<Item> items(N);
	for(ll i=0; i<N; i++){
		cin >> items[i].value;
		cin >> items[i].weight;
		items[i].index = i;
	}

	//分枝限定法で探索
	KnapsackBB knapsack(items, W);
	ll opt_value = knapsack.solve();
	cout << opt_value << endl;

	return 0;
}



Measured memory_bytes: 3184