#include <iostream>
#include <fstream>

using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");

struct energii
{
    int val, cost;
};

energii v[501];

int suma[15001];

int main()
{
    int Gen, W, max, i, j=0, pos;
    f>>Gen>>W;
    for(i=1; i<=Gen; i++) f>>v[i].val>>v[i].cost;
    max=0;
    pos=15001;
    for(i=1; i<=Gen; i++)
    {
        for(j=max; j>=1; j--)
            if(suma[j]!=0)
            {
                if(suma[j+v[i].val]>suma[j]+v[i].cost || suma[j+v[i].val]==0)
                {
                    suma[j+v[i].val]=suma[j]+v[i].cost;
                    if(j+v[i].val<=pos && j+v[i].val>=W) pos=v[i].val;
                }
            }

        max=j+v[i].val;
        if(suma[v[i].val]>v[i].cost || suma[v[i].val]==0)
            suma[v[i].val]=v[i].cost;
    }

    if(pos==15001) g<<"-1";
    else g<<suma[pos];
    return 0;
}