#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
template<class T>bool chmax(T &a, const T &b) { if (a<b) { a=b; return true; } return false; }
template<class T>bool chmin(T &a, const T &b) { if (b<a) { a=b; return true; } return false; }
#define vi vector<int>
#define vl vector<ll>
#define vii vector<pair<int,int>>
#define vll vector<pair<ll,ll>>
#define vvi vector<vector<int>>
#define vvl vector<vector<ll>>
#define vvii vector<vector<pair<int,int>>>
#define vvll vector<vector<pair<ll,ll>>>
#define vst vector<string>
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define mkunique(x) sort(all(x));(x).erase(unique(all(x)),(x).end())
#define fi first
#define se second
#define mp make_pair
#define si(x) int(x.size())
const int mod=998244353,MAX=300005;
const ll INF=15LL<<58;

ll dp[1005];

int main(){
    
    std::ifstream in("text.txt");
    std::cin.rdbuf(in.rdbuf());
    cin.tie(0);
    ios::sync_with_stdio(false);
    
    ll N,M;cin>>N>>M;
    vll S(N);
    for(int i=0;i<N;i++){
        cin>>S[i].fi>>S[i].se;
    }
    sort(all(S));
    reverse(all(S));
    for(int i=0;i<1005;i++){
        dp[i]=-INF;
    }
    dp[M]=0;
    for(int i=0;i<N;i++){
        for(int j=0;j<=M;j++){
            if(S[i].fi<=j){
                chmax(dp[(j-S[i].fi)/2],dp[j]+S[i].se);
            }
        }
    }
    ll ans=-INF;
    for(int j=0;j<=M;j++) chmax(ans,dp[j]);
    cout<<ans<<endl;
}