#include<fstream>
using namespace std;
ifstream fin("lapte.in");
ofstream fout("lapte.out");
int g,w,i,j;
int e[10005],c[10005];
int d[10005][10005];
int main(){
    fin>>g>>w;
    for(i=1;i<=g;i++){
        fin>>e[i]>>c[i];
    }
    for(i=1;i<=g;i++){
        for(j=1;j<=w;j++){
            d[i][j]=1000000000;
            if(e[i]<=j){
                d[i][j]=min(d[i-1][j],d[i-1][j-e[i]]+c[i]);
            }
            else{
                d[i][j]=min(d[i-1][j],c[i]);
            }
        }
    }
    if(d[g][w]==1000000000){
        fout<<"-1";
        return 0;
    }
    fout<<d[g][w];
    return 0;
}