#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
using ll=long long;

int main()
{
	ll n,m;
	cin>>n>>m;
	vector<pair<ll,ll>> cd(n);
	for(int i=0;i<n;i++)cin>>cd[i].first>>cd[i].second;
	sort(cd.begin(),cd.end(),[](auto x,auto y)->bool{
		return x.first>y.first;
	});
	ll ans2=0;
	while((!cd.empty())&&cd.back().first==0){
		ans2+=cd.back().second;
		cd.pop_back();
		n--;
	}

	vector<vector<ll>> crt(m+1,vector<ll>(11));
	for(int i=0;i<n;i++){
		
		vector<vector<ll>> nxt(m+1,vector<ll>(11));
		for(int j=0;j<=m;j++){
			for(int k=0;k<=10;k++){
				ll x=(cd[i].first<<k);
				nxt[j][k]=max(nxt[j][k],crt[j][k]);
				if(k<10&&j+x<=m){
					nxt[j+x][k+1]=max(nxt[j+x][k+1],crt[j][k]+cd[i].second);
				}
			}
		}
		swap(crt,nxt);
	}
	ll ans=0;
	for(int i=0;i<=m;i++)for(int j=0;j<=10;j++)ans=max(ans,crt[i][j]);
	cout<<ans+ans2<<endl;
	
    return 0;
}