#include<fstream>
using namespace std;
int g,w,c,i,a[10001],e,b[10001],in,cmin,q;
ifstream f("energii.in");
ofstream h("energii.out");
int main ()
{
	f>>g>>w;
	q=1;
	for(i=1;i<=g*2;i++)
		f>>a[i];
	for(i=1;i<=g*2-1;i=i+2)
	{
		if(a[i]==w)
		{
			h<<a[i+1];
			return 0;
		}
		if(a[i]>w)
		{
			b[q++]=a[i];
			b[q++]=a[i+1];
		}
	}
	cmin=b[2];
	in=b[1];
	for(i=3;i<=2*g-1;i=i+2)
		if(in>b[i])
		{
			in=b[i];
			cmin=b[i+1];
		}
		if(in>=w)
			{
				h<<cmin;
				return 0;
			}
	for(i=1;i<=2*g-1&&w>=e;i=i+2)
	{
		e=e+a[i];
		c=c+a[i+1];
		if(w<=e)
		{
			h<<c;
			return 0;
		}
	}
	h<<"-1";
	return 0;
	
}