#include <iostream>
#include <fstream>
using namespace std;
int w,g,egi,cgi,mn,nr=0;
int main()
{
    ifstream f("energii.in");
    ofstream gout("energii.out");
    f>>g;
    f>>w;
    for (int i=1;i<=g;i++)
    {
        f>>egi>>cgi;
    }
    for (int i=1;i<=g;i++)
    {
        if (egi==w) {nr++;mn=cgi;}
    }
    if (nr!=0) gout<<mn;
    else gout<<-1;
    return 0;
}