#include <fstream>
using namespace std;
double gen[1001][3], n;
int rezolva(){
    int g=0;
    double max=0,aux=0;
    for(int i=1;i<=n;i++){
            if(gen[i][0]==-1){aux=gen[i][1]/gen[i][2];
            if(max<aux){ max=aux;g=i;}};
            
            }
    return g;
    }

int main(){
    int w,h=0,x=0;
    
    double a, eng=0,cost=0;
    ifstream in("energii.in");
    in>>n;in>>w;
    for(int i=1;i<=n;i++){gen[i][0]=-1;in>>gen[i][1];in>>gen[i][2];} in.close();
    do{
    h=rezolva();
    eng+=gen[h][1];
    cost+=gen[h][2];
    gen[h][0]=9;
    x++;
    if(x>n){cost=-1;break;}
    }while(eng<w);
    
    ofstream out("energii.out");
    out<<cost;
    out.close();
    return 0;    
}