#include <bits/stdc++.h>
using namespace std;
using ll = long long;
struct Item {
ll w, v;
};
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int N;
ll M;
cin >> N >> M;
vector<Item> a(N);
for (int i = 0; i < N; i++) cin >> a[i].w >> a[i].v;
int n1 = N / 2;
int n2 = N - n1;
vector<Item> A(a.begin(), a.begin() + n1);
vector<Item> B(a.begin() + n1, a.end());
vector<pair<ll,ll>> SA;
for (int mask = 0; mask < (1 << n1); mask++) {
ll w = 0, v = 0;
for (int i = 0; i < n1; i++)
if (mask & (1 << i)) w += A[i].w, v += A[i].v;
if (w <= M) SA.push_back({w, v});
}
vector<pair<ll,ll>> SB;
for (int mask = 0; mask < (1 << n2); mask++) {
ll w = 0, v = 0;
for (int i = 0; i < n2; i++)
if (mask & (1 << i)) w += B[i].w, v += B[i].v;
if (w <= M) SB.push_back({w, v});
}
sort(SB.begin(), SB.end());
vector<pair<ll,ll>> goodB;
ll best = -1;
for (auto &p : SB) {
if (p.second > best) {
best = p.second;
goodB.push_back(p);
}
}
ll ans = 0;
for (auto &x : SA) {
ll wA = x.first, vA = x.second;
ll remain = M - wA;
int l = 0, r = (int)goodB.size() - 1, pos = -1;
while (l <= r) {
int m = (l + r) / 2;
if (goodB[m].first <= remain) pos = m, l = m + 1;
else r = m - 1;
}
if (pos != -1)
ans = max(ans, vA + goodB[pos].second);
else
ans = max(ans, vA);
}
cout << ans;
return 0;
}
