#include <fstream>
#include <algorithm>
using namespace std;
ifstream cin("energii.in");
ofstream cout("energii.out");
struct gen{
int c,p;
}g[5001];
int n,w,dp[10001];
const int oo=(1<<30);
bool cmp(gen a,gen b)
{
    return (a.c/a.p)<(b.c/b.p);
}
int main()
{
    cin>>n>>w;
    for(int i=1;i<=n;i++)
        cin>>g[i].p>>g[i].c;
        for(int i=1;i<=10000;i++)
            dp[i]=oo;
    sort(g+1,g+n+1,cmp);
    for(int i=1;i<=n;i++)
    {
        for(int j=1;j<=10001;j++)
            if(g[i].p<=j)
        dp[j]=min(dp[j],dp[j-g[i].p]+g[i].c);
    }
    int minn=oo;
    for(int i=w;i<=10000-8;i++)
        minn=min(minn,dp[i]);
    cout<<(minn==oo?-1 : minn);
    return 0;
}