#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000000
#define Inf64 1000000000000000001LL

int main(){
	
	long long n,m;
	cin>>n>>m;
	vector<pair<long long,long long>> t;
	long long ans = 0;
	rep(i,n){
		long long c,d;
		cin>>c>>d;
		if(c==0)ans += d;
		else t.emplace_back(c,d);
	}
	sort(t.begin(),t.end());
	vector<long long> dp(m+1,0);
	rep(i,t.size()){
		for(int j=m;j>=0;j--){
			if(j*2 + t[i].first <= m){
				dp[j*2 + t[i].first] = max(dp[j*2 + t[i].first],dp[j]+t[i].second);
			}
			
		}
	}
	long long tt = 0;
	rep(i,m+1)tt = max(tt,dp[i]);
	cout<<ans+tt<<endl;
	return 0;
}