#include <bits/stdc++.h>
using namespace std;

#define rep(i, l, r) for (int i = (int)(l); i<(int)(r); i++)
#define ll long long

ll INF = 4e18;

int main() {
    int N, M; cin >> N >> M;
    vector<pair<int, int>> CD(N);
    rep(i, 0, N) {
        cin >> CD[i].first >> CD[i].second;
    }
    sort(CD.rbegin(), CD.rend());
    vector<unordered_map<int, ll>> dp(30);
    dp[0][0] = 0;
    rep(i, 0, N) {
        for (int j = 29; j >= 0; j--) {
            for (auto[key, val] : dp[j]) {
                // cout << i << " " << j << " "  << key << " : " << val << endl;
                //選ぶ
                ll nkey = key + (1LL<<j) * CD[i].first;
                if (nkey <= M) {
                    if (dp[j+1].contains(nkey)) {
                        dp[j+1][nkey] = max(dp[j+1][nkey], val + CD[i].second);
                    }
                    else dp[j+1][nkey] = val + CD[i].second;
                }
            }
        }
    }
    ll ans = 0;
    rep(i, 0, 30) {
        for (auto[key, val] : dp[i]) ans = max(ans, val);
    }
    cout << ans << endl;
}