#include <fstream>

using namespace std;
ifstream cin("energii.in");
ofstream cout("energii.out");
double z[10001];
int a,b,i,j,x[10001],y[10001],s,sg;
int main()
{cin>>a>>b;
for(i=1;i<=a;i++)
    {cin>>x[i]>>y[i];
    z[i] = y[i]/(double)x[i];
    }
for(i=1;i<a;i++)
    for(j=i+1;j<=a;j++)
        if(z[i]>z[j])
    {swap(x[i],x[j]);
    swap(y[i],y[j]);
    }
for(i=1;i<=a;i++)
    if(s<b)
{s=s+x[i];
sg = sg+y[i];
}
if(sg>=b)
    cout << sg;
else
	cout<<"-1";
    return 0;
}