#include <iostream>
#include <fstream>
#include <stdio.h>
using namespace std;
int a,b,e,g,i,maxi,nr;
int main()
{
    ifstream f ("energii.in");
    f>>g;
    f>>e;
    while(!f.eof())
        {
        f>>a;
        f>>b;
        if((a<=e)&&(b>e))
            nr=b;
        }
        ofstream h ("energii.out");

        if(nr==0)
            h<<-1;
        else h<<nr;
f.close();
h.close();
    return 0;
}