#include <bits/stdc++.h>
//#include <atcoder/modint>

using namespace std;
//using namespace atcoder;
using ll = long long;
//using mint = modint998244353;

int main(){
    cin.tie(nullptr);
    ios_base::sync_with_stdio(false);

    ll N, M, ans=0, c, d;
    cin >> N >> M;
    vector<pair<ll, ll>> v;

    for (int i=0; i<N; i++){
        cin >> c >> d;
        if (c == 0) ans += d;
        else v.push_back({c, d});
    }
    sort(v.rbegin(), v.rend());

    vector<ll> pw(24);
    pw[0] = 1;
    for (int i=1; i<=23; i++) pw[i] = pw[i-1] * 2;

    vector dp(24, vector<ll>(M+1));
    for (auto [c, d] : v){
        vector pd(24, vector<ll>(M+1));
        for (int i=0; i<=23; i++){
            for (int j=0; j<=M; j++){
                pd[i][j] = max(pd[i][j], dp[i][j]);
                ll cost = c * pw[i];
                if (i+1<=23 && j+cost <= M) pd[i+1][j+cost] = max(pd[i+1][j+cost], dp[i][j]+d);
            }
        }
        swap(dp, pd);
    }
    ll mx=0;
    for (int i=0; i<=23; i++){
        for (int j=0; j<=M; j++) mx = max(mx, dp[i][j]);
    }
    cout << mx+ans << endl;

    return 0;
}