#include<stdio.h>
FILE *in,*out;
int i,g,w,v[5000][3];
long long s;
int main()
{
    in=fopen("energii.in","rt");
    out=fopen("energii.out","wt");
    fscanf(in,"%d%d",&g,&w);
    for(i=1;i<=g;i++)
    {
        fscanf(out,"%d%d",&v[i][1],&v[i][2]);
        s+=v[i][1];
    }
    if(s<w)
        fprintf(out,"-1");
    return 0;
}