#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

using mint = modint998244353;

void debug_mint1(vector<mint> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        cerr << vec[i].val() << " ";
    }
    cerr << endl;
}

void debug_mint2(vector<vector<mint>> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        for (int j = 0; j < vec[i].size(); j++) {
            cerr << vec[i][j].val() << " ";
        }
        cerr << endl;
    }
}

int main() {
    ll N, M;
    cin >> N >> M;
    vector<ll> C(N);
    vector<ll> D(N);
    for (ll i = 0; i < N; i++) {
        cin >> C[i] >> D[i];
    }
    // カードを使ったか、使わなかったかを管理して DP すればよい？
    // ただし、0 のカードだけは例外的に最後にまとめて使う
    ll zero_val = 0;
    vector<pll> p(0);
    for (ll i = 0; i < N; i++) {
        if (C[i] > 0) {
            p.push_back(make_pair(C[i], D[i]));
        } else {
            zero_val += D[i];
        }
    }
    sort(all(p));
    reverse(all(p));
    ll INF = 1000000000000000023;
    ll len = p.size();
    vector dp(M + 1, vector<ll>(11, -INF));
    dp[0][0] = 0;
    for (ll i = 0; i < len; i++) {
        vector ndp(M + 1, vector<ll>(11, -INF));
        for (ll j = 0; j <= M; j++) {
            ll now_cost = p[i].first;
            for (ll k = 0; k < 10; k++) {
                if (dp[j][k] < 0) {
                    now_cost *= 2;
                    continue;
                }
                if (j + now_cost <= M) {
                    ndp[j + now_cost][k + 1] =
                        max(ndp[j + now_cost][k + 1], dp[j][k] + p[i].second);
                }
                ndp[j][k] = max(ndp[j][k], dp[j][k]);
                now_cost *= 2;
            }
        }
        for (ll j = 0; j <= M; j++) {
            for (ll k = 0; k <= 10; k++) {
                dp[j][k] = ndp[j][k];
            }
        }
    }
    ll ans = -INF;
    for (ll j = 0; j <= M; j++) {
        for (ll k = 0; k <= 10; k++) {
            ans = max(ans, dp[j][k]);
        }
    }
    cout << ans + zero_val << endl;
}