#include <iostream>
#include <fstream>
using namespace std;
int g,w,a,b,c,x,y,j;
int main()
{
    ifstream f("energii.in");
    ofstream gout("energii.out");
    f>>g;
    f>>w;
    for (int i=1;i<=g;i++)
    {
        f>>a>>b;
    }
    c=9999999999;
    for (int i=1;i<=g;i++)
    {
        j=i;
        x=0;
        y=0;
        while (x<w)
        {
            x=x+a;
            y=y+b;
        }
        if (x>=w&&y<c) c=y;
    }
    if (c==9999999999) c=-1;
    gout<<c;
    return 0;
}