#include <fstream>
#include <iostream>
using namespace std;

int main()
{
    ifstream f ("energii.in");
    ofstream h ("energii.out");
    int g,w,i,j ;
    f >> g ;
    int a[g+1][3] ;
    f >> w ;

    for (i=1;i<=g;i++)
        for (j=1;j<=2;j++)
        {f >> a[i][j] ;}

        j = 1;
        int v[g+1];
int k=0;
    for (i=1;i<=g;i++)

    {
         if ( (a[i][1] / w) >= 1) v[++k] = a[i][1] ;
         //else v[i] = -1 ;
    }

     int cost[g] ,q=0;
            for (i=1;i<=g;i++)

                 {int ok=0;
                  for(j=1;j<=k;j++)
                      if (a[i][1] == v[j] )ok=1;
                      if(ok) cost[++q] = a[i][2] ; }

                    int min = 10001;
//for (i=1;i<=k;i++) cout << v[i] ; cout <<'\n';
//for (i=1;i<=q;i++) cout << cost[i] ; cout <<'\n';

       for (i=1;i<=q;i++)
       { if ( cost[i] < min ){ min = cost[i] ; }}


if (min != 10001)
       h<<min ;
       else h << -1 ;

     f.close();
     h.close();
    return 0;
}