#include <fstream>

using namespace std;

int G,W,V[10002];
ifstream fin("energii.in");
ofstream fout("energii.out");

int citire()
{
    int i,m=0;
    fin>>G>>W;
    for(i=0;i<G;i++)
    {
        fin>>V[i];
        if(V[i] > m)
            m = V[i];
        fin>>V[i];
        if(V[i] > m)
            m = V[i];
    }
    return m;
}

int main()
{
    int m;
    m = citire();
    if(m >= W)
        fout<<m;
    else
        fout<<-1;
    fout<<"\n";
}