#include <iostream>
#include <fstream>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int main()
{
   int G,W,Cmin=2000000000,EGi,CGi,i,aux=0;
   fin>>G>>W;
   for(i=0;i<=G;i++)
   {
       fin>>EGi>>CGi;
       if(EGi>=W)
       {
            aux=EGi;
           Cmin=CGi;
       }

       if(CGi>=W && Cmin>CGi)
            Cmin=CGi;
   }
   if(Cmin==2000000000)
    Cmin=-1;
   fout<<Cmin;
}