// #pragma GCC target("avx2")
// #pragma GCC optimize("O3")
// #pragma GCC optimize("unroll-loops")


#include<bits/stdc++.h>
using namespace std;
using uint = unsigned int;
using ll = long long;
using ull = unsigned long long;
using ld = long double;
template<class T> using V = vector<T>;
template<class T> using VV = V<V<T>>;
template<class T> using VVV = V<VV<T>>;
template<class T> using VVVV = VV<VV<T>>;
#define rep(i,n) for(ll i=0ll;(i)<(n);(i)++)
#define REP(i,a,n) for(ll i=(a);(i)<(n);(i)++)
#define rrep(i,n) for(ll i=(n)-1;(i)>=(0ll);(i)--)
#define RREP(i,a,n) for(ll i=(n)-1;(i)>=(a);(i)--)
const long long INF = (1LL << 60);
const long long mod99 = 998244353;
const long long mod107 = 1000000007;
const long long mod = mod99;
#define eb emplace_back
#define be(v) (v).begin(),(v).end()
#define all(v) (v).begin(),(v).end()
#define foa(i,v) for(auto& (i) : (v))
#define UQ(v) sort(be(v)), (v).erase(unique(be(v)), (v).end())
#define UQ2(v,cmp) sort(be(v)), (v).erase(unique(be(v),cmp), (v).end())
#define UQ3(v,cmp) sort(be(v),cmp), (v).erase(unique(be(v)), (v).end())
#define UQ4(v,cmp,cmp2) sort(be(v), cmp), (v).erase(unique(be(v),cmp2), (v).end())
#define LB(x,v) (lower_bound(be(v),(x))-(v).begin())
#define LB2(x,v,cmp) (lower_bound(be(v),(x),(cmp))-(v).begin())
#define UB(x,v) (upper_bound(be(v),(x))-(v).begin())
#define UB2(x,v,cmp) (upper_bound(be(v),(x),(cmp))-(v).begin())
#define dout()  cout << fixed << setprecision(20)
#define randinit() srand((unsigned)time(NULL))

template<class T, class U> bool chmin(T& t, const U& u) { if (t > u){ t = u; return 1;} return 0; }
template<class T, class U> bool chmax(T& t, const U& u) { if (t < u){ t = u; return 1;} return 0; }


ll Rnd(ll L=0, ll R=mod99){return rand()%(R-L)+L;}



void solve(){
    ll n,m;
    cin >> n >> m;
    ll ans = 0;
    V<pair<ll,ll>> c;
    rep(i,n){
        ll x,y;
        cin >> x >> y;
        if(x == 0) ans += y;
        else c.eb(-x, -y);
    }
    sort(be(c));
    V<pair<ll,ll>> d = c;
    for(auto&[x,y]:c) x = -x, y = -y;
    n = c.size();
    map<tuple<ll,ll,ll>, ll> mp;
    auto dfs = [&](auto&&dfs, ll idx, ll rest, ll count) -> ll {
        // cout << idx << " " << rest << " " << count << endl;
        if(idx == n or rest < (1<<count)) return 0;
        if(mp.count({idx, rest, count})) return mp[{idx, rest, count}];
        
        ll ans = 0;
        ll x = dfs(dfs, idx+1, rest, count);
        chmax(ans, x);
        {
            auto[a,b] = c[idx];
            ll re = rest - (a << count);
            pair<ll,ll> xx = {-re, -INF};
            ll id = LB(xx, d);
            chmax(id, idx+1);
            ll y = b + dfs(dfs, id, re, count+1);
            chmax(ans, y);
        }
        // cout << idx << " " << rest << " " << count << " " << ans << endl;
        return mp[{idx, rest, count}] = ans;
    };
    
    cout << ans + dfs(dfs, 0, m, 0) << endl;
    
}





int main(){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    int t=1;
    // cin >> t;
    rep(i,t) solve();
}