#include <iostream>
#include <fstream>
using namespace std;

ifstream fin ("energii.in");
ofstream fout ("energii.out");


int main()
{
    int n, i, e, cost[100], cant[100], s;
    s = 0;
    fin >> n;
    fin >> e;
    for (i = 1; i <= n; i ++)   {
        fin >> cant[i] >> cost[i];
        s += cant[i];
    }
    if (s < e)
        fout <<"-1";

}