#include <bits/stdc++.h>
#define int long long
#define pii pair<int,int>
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n) FOR(i,0,n)
#define ALL(c) (c).begin(),(c).end()
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
#define MINF(a) memset(a,0x3f,sizeof(a))
#define POW(n) (1LL<<(n))
#define IN(i,a,b) (a <= i && i <= b)
using namespace std;
template <typename T> inline bool CHMIN(T& a,T b) { if(a>b) { a=b; return 1; } return 0; }
template <typename T> inline bool CHMAX(T& a,T b) { if(a<b) { a=b; return 1; } return 0; }
template <typename T> inline void SORT(T& a) { sort(ALL(a)); }
template <typename T> inline void REV(T& a) { reverse(ALL(a)); }
template <typename T> inline void UNI(T& a) { sort(ALL(a)); a.erase(unique(ALL(a)),a.end()); }
template <typename T> inline void LB(vector<T>& v, T& a) { return *lower_bound(ALL(v),a); }
template <typename T> inline void LBP(vector<T>& v, T& a) { return lower_bound(ALL(v),a) - v.begin(); }
template <typename T> inline void UB(vector<T>& v, T& a) { return *upper_bound(ALL(v),a); }
template <typename T> inline void UBP(vector<T>& v, T& a) { return upper_bound(ALL(v),a) - v.begin(); }
template <typename T1, typename T2> ostream& operator<< (ostream& os, const pair<T1,T2>& p) { os << p.first << " " << p.second; return os; }
template <typename T1, typename T2> istream& operator>> (istream& is, pair<T1,T2>& p) { is >> p.first >> p.second; return is; }
template <typename T> ostream& operator<< (ostream& os, const vector<T>& v) { REP(i,v.size()) { if (i) os << " "; os << v[i]; } return os; }
template <typename T> istream& operator>> (istream& is, vector<T>& v) { for(T& in : v) is >> in; return is; }
template <typename T = int> vector<T> make_v(size_t a) { return vector<T>(a); }
template <typename T, typename... Ts> auto make_v(size_t a, Ts... ts) { return vector<decltype(make_v<T>(ts...))>(a,make_v<T>(ts...)); }
template< typename T, typename V > typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) { t = v; }
template< typename T, typename V > typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) { for(auto &e : t) fill_v(e, v); }
const int MOD = 1000000007;
const int INF = 0x3f3f3f3f3f3f3f3f;
const double EPS = 1e-10;

int knapsack_huge(vector<int> v, vector<int> w, int W) {
  int N = v.size(), N2 = N / 2, V = accumulate(v.begin(), v.end(), 0LL);
  vector<pair<int, int>> ps;
  for (int i = 0; i < 1 << N2; i++) {
    int sv = 0, sw = 0;
    for (int j = 0; j < N2; j++) {
      if (i >> j & 1) {
        sv += v[j];
        sw += w[j];
      }
    }
    ps.emplace_back(sw, sv);
  }
  sort(ps.begin(), ps.end());
  int m = 1;
  for (int i = 1; i < 1 << N2; i++) {
    if (ps[m - 1].second < ps[i].second) {
      ps[m++] = ps[i];
    }
  }
  int res = 0;
  for (int i = 0; i < 1 << (N - N2); i++) {
    int sv = 0, sw = 0;
    for (int j = 0; j < N - N2; j++) {
      if (i >> j & 1) {
        sv += v[N2 + j];
        sw += w[N2 + j];
      }
    }
    if (sw <= W) {
      int tv = (lower_bound(ps.begin(), ps.begin() + m, make_pair(W - sw, V + 1)) - 1)->second;
      res = max(res, sv + tv);
    }
  }
  return res;
}

signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(10);

  int N,W;
  cin >> N >> W;
  vector<int> v(N),w(N);
  REP(i,N) cin >> v[i] >> w[i];
  cout << knapsack_huge(v,w,W) << endl;

  return 0;
}


Measured memory_bytes: 19536