#include<iostream>
#include<fstream>
using namespace std;
int main()
{
	int g,w,min,a,b,i,s=0;
	ifstream f("energii.in");
	ofstream r("energii.out");
	f>>g;f>>w;
	min=5001;
	for(i=1;i<=g;i++)
	{
		f>>a;f>>b;
		s=s+a;
		if(a>=w&&b<=min)
			min=b;
	}
	if(s<=8)
		r<<-1;
	else
	r<<min;
	return 0;
}