#include <iostream>
#include <fstream>
#define MaxG 1002
#define MaxW 5002
#define undefined -1
using namespace std;
ifstream f("energii.in");
ofstream fout("energii.out");
typedef long long ll;
int g,w;
ll e[MaxG],c[MaxW];
ll m[MaxG][MaxW];
bool sol=false;
ll rez(int g,int w)
{
    if(w<=0)
    {
        sol=true;
        return 0;
    }
    if(g==0)
        return 100000000;
    if(m[g][w]!= undefined) return m[g][w];
    ll rez1 = rez(g-1,w);
    ll rez2 = rez(g-1,w-e[g])+c[g];
    m[g][w]=min(rez1,rez2);
    return m[g][w];
}

int main()
{
    f>>g>>w;
    for(int i=1;i<=g;i++)
        f>>e[i]>>c[i];
    for(int i=1;i<=g;i++)
        for(int j=1;j<=w;j++)
            m[i][j]=undefined;
    ll solutie = rez(g,w);
    fout<<(sol? solutie : -1);
    f.close();
    fout.close();
    return 0;
}