#include <bits/stdc++.h>
using namespace std;
template <class F> class y_combinator {
    F f;

   public:
    y_combinator(F&& f) : f(std::forward<F>(f)) {}
    template <class... Args> auto operator()(Args&&... args) const { return f(*this, std::forward<Args>(args)...); }
};
using ll = long long;
using ld = long double;
using u64 = uint64_t;
using vi = vector<int>;
using vl = vector<ll>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
template <class T, class U = std::less<T>> using prique = std::priority_queue<T, std::vector<T>, U>;
inline constexpr int popcnt(u64 x) noexcept { return __builtin_popcountll(x); }
inline ll floor_div(ll a, ll b) noexcept { return a / b - (a % b && (a ^ b) < 0); }
inline ll ceil_div(ll a, ll b) noexcept { return floor_div(a + b - 1, b); }
template <class T> bool chmin(T& x, const T& y) noexcept { return (x > y ? x = y, true : false); }
template <class T> bool chmax(T& x, const T& y) noexcept { return (x < y ? x = y, true : false); }
template <class T> void dedup(std::vector<T>& v) { std::sort(std::begin(v), std::end(v)), v.erase(std::unique(std::begin(v), std::end(v)), std::end(v)); }
template <class F> ll bisect(ll ok, ll ng, const F& f) { while (abs(ok - ng) > 1) { ll mid = (ok + ng) / 2; (f(mid) ? ok : ng) = mid; } return ok; }
template <class F> ld bisect_real(ld ok, ld ng, const F& f, int iter = 80) { while (iter--) { ld mid = (ok + ng) / 2.; (f(mid) ? ok : ng) = mid; } return ok; }
inline void SCAN() {}
template <class H, class... T> inline void SCAN(H& h, T&... t) { std::cin >> h, SCAN(t...); }
#define INT(...) int __VA_ARGS__; SCAN(__VA_ARGS__)
#define LL(...) long long __VA_ARGS__; SCAN(__VA_ARGS__)
#define LD(...) long double __VA_ARGS__; SCAN(__VA_ARGS__)
#define STR(...) std::string __VA_ARGS__; SCAN(__VA_ARGS__)
#define CHAR(...) char __VA_ARGS__; SCAN(__VA_ARGS__)
#define VEC(type, name, size) std::vector<type> name(size); for (int i = 0; i < (int)size; i++) SCAN(name[i]);
#define VV(type, name, h, w) std::vector<std::vector<type>> name(h, std::vector<type>(w)); for (int i = 0; i < (int)h; i++) for (int j = 0; j < (int)w; j++) SCAN(name[i][j]);
#define overload4(a, b, c, d, e, ...) e
#define rep1(a) for (long long _i = 0; _i < (a); _i++)
#define rep2(i, a) for (long long i = 0; i < (a); i++)
#define rep3(i, a, b) for (long long i = (a); i < (b); i++)
#define rep4(i, a, b, c) for (long long i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define rrep(i, a, b, c) for (long long i = (a); i > (b); i += (c))
#define all(x) std::begin(x), std::end(x)
#define rall(x) std::rbegin(x), std::rend(x)
#define len(x) (long long)(size(x))
#define pb push_back

int main() {
	std::ios_base::sync_with_stdio(false);
	std::cin.tie(nullptr);
	INT(N,M);
	vector<pair<ll,ll>> G;
	ll sum = 0;
	rep(i, N) {
		INT(c,d);
		if(c==0) sum += d;
		else {
			G.pb({c,d});
		}
	}
	N=G.size();
	sort(rall(G));
	vector dp(N+1,vector<pair<ll,ll>>(12,{1e18,-1}));
	dp[0][0]={0,0};
	rep(i, N){
		dp[i+1]=dp[i];
		rep(j,11) if(dp[i][j].second!=-1) {
			ll cst=dp[i][j].first+(G[i].first<<j);
			if(cst<=M && chmax(dp[i+1][j+1].second,dp[i][j].second+G[i].second)) {
				dp[i+1][j+1].first=cst;
			}
		}
	}
	ll ans = 0;
	rep(i,12)if(dp[N][i].first<=M)chmax(ans,dp[N][i].second+sum);
	cout<<ans<<"\n";
}