#include <iostream>
#include <fstream>
using namespace std;
int v[10002][2],i,c,j,G,W,n,d,x,y,z;
int main()
{
    i=1;
    ifstream f("energii.in");
    ofstream g("energii.out");
    f>>G>>W;
    while (f>>v[i][1]>>v[i][2])
    {
        c=c+v[i][1];
        d=d+v[i][2];
        if(v[i][1]==W) {g<<v[i][2];break;}
        i++;
    }
    if(c<W) g<<"-1";
    else if(c==W) g<<d;
      else
        { n=i;
            x=0;y=1;z=y;
            while(x<W)
            {
                break;


            }
        }
    cout.flush();
    return 0;
}