#include <iostream>
#include <vector>
#include <cstdio>
using namespace std;
int n,m;
vector<int> f(40001,0);
int med[21][21]={0};
vector<int> v,w;
void deal(int i,int j)
{
	if(med[i][j]==0)
		return ;
	if(med[i][j]==1)
	{
		v.push_back(i);
		w.push_back(j);
		return ;
	}
	int k=1,s=1;
	while(s<med[i][j])
	{
		v.push_back(i*k);
		w.push_back(j*k);
		k<<=1;
		s+=k; 
	}
	v.push_back((med[i][j]-s+k)*i);
	w.push_back((med[i][j]-s+k)*j);
}
void in()
{
	cin>>n>>m;
	int a,b;
	for(int i=1;i<=n;i++)
	{
		cin>>a>>b;
		++med[a][b];
	}
	for(int i=1;i<=20;i++)
		for(int j=1;j<=20;j++)
			deal(i,j);
}
void bag()
{
	for(int i=0;i<v.size();i++)
		for(int j=m;j>=v[i];j--)
			f[j]=max(f[j],f[j-v[i]]+w[i]);
	cout<<f[m];
}
int main()
{
	freopen ("crazytime.in","r",stdin);
	freopen ("crazytime.out","w",stdout);
	in();
	bag();
	return 0;
}