#include <fstream>
using namespace std;
ifstream eu("energii.in");
ofstream tu("energii.out");
#define Nmax 1005
#define oo 1<<17
int DP[Nmax][5005],E[Nmax],C[Nmax],N,W;
void Read()
{
    eu>>N>>W;
    for(int i=1;i<=N;i++)
        eu>>E[i]>>C[i];

    for(int i=0;i<=N;i++)
        for(int j=1;j<=W;j++)
            DP[i][j]=oo;
}
void Solve()
{
    for(int i=1;i<=N;i++)
        for(int j=1;j<=W;j++)
            if(E[i]<=j)
                DP[i][j]=min(DP[i-1][j],DP[i-1][j-E[i]]+C[i]);
            else
                DP[i][j]=min(DP[i-1][j],C[i]);
}
void Print()
{
    if(DP[N][W]==oo)
        tu<<"-1"<<"\n";
    else
        tu<<DP[N][W]<<"\n";
}
int main()
{
    Read();
    Solve();
    Print();
    return 0;
}