#include <bits/stdc++.h>
#define rep(i, p, n) for (ll i = p; i < (ll)(n); i++)
#define rep2(i, p, n) for (ll i = p; i >= (ll)(n); i--)
using namespace std;
using ll = long long;
using ld = long double;
const double pi = 3.141592653589793;
const long long inf = 2 * 1e9;
const long long linf = 4 * 1e18;
const ll mod1 = 1000000007;
const ll mod2 = 998244353;
template <class T>
inline bool chmax(T &a, T b)
{
    if (a < b)
    {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T &a, T b)
{
    if (a > b)
    {
        a = b;
        return 1;
    }
    return 0;
}

// atcoder
#include <atcoder/all>
using namespace atcoder;
using mint1 = modint1000000007;
using mint2 = modint998244353;

vector<pair<ll, ll>> base = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};

int main()
{

    //////////////////
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    //////////////////

    ll N, M;
    cin >> N >> M;
    vector<pair<ll, ll>> li;
    ll ans = 0;
    rep(i, 0, N)
    {
        ll C, D;
        cin >> C >> D;
        if (C == 0)
        {
            ans += D;
            continue;
        }
        li.push_back({C, D});
    }
    N = li.size();
    sort(li.begin(), li.end());
    reverse(li.begin(), li.end());
    vector<ll> dp(M+1), ndp(M+1);
    rep(i, 0, N)
    {
        rep(j, 0, M + 1)
        {
            chmax(ndp.at(j), dp.at(j));
            if (j - li.at(i).first >= 0)
            {
                chmax(ndp.at((j - li.at(i).first) / 2), dp.at(j) + li.at(i).second);
            }
        }
        rep(j, 0, M+1) {
            dp.at(j) = ndp.at(j);
            ndp.at(j) = 0;
        }
    }
    ll ma = 0;
    rep(i, 0, M + 1)
    {
        chmax(ma, dp.at(i));
    }
    cout << ans + ma;
}