#include <fstream>
#include <algorithm>

using namespace std;

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

struct per{
    double e, cost, cost1;
}s[1002];

inline bool Cmp(per a, per b){
    if(a.cost1 < b.cost1) return 1;
    else if(a.cost1 == b.cost1){
        if(a.e < b.e) return 1;
        else if(a.e == b.e) return a.cost < b.cost;
    }
    return 0;
}

int main()
{
    int w, g;
    fin >> g >> w;
    for(int i = 1; i <= g; i++){
        fin >> s[i].e >> s[i].cost;
        s[i].cost1 = double(s[i].cost / s[i].e);
    }
    sort(s + 1, s + g + 1, Cmp);
    int suma = 0;
    for(int i = 1; i <= g; i++){
        if(suma + s[i].cost <= w)
            suma += s[i].cost;
        else{
            while(suma <= w)
                suma += s[i].cost1;
        }
    }
    if(suma < w) fout << -1;
    else fout << suma;
    return 0;
}