#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");

const int Gmax = 1005;
const int Wmax = 5005;
const int inf = 2000000000;
int E[Gmax],C[Gmax],dp[Gmax][Wmax];
int W,G;


int main()
{
    int i,j;
    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++)
            dp[i][j] = inf;
    dp[1][E[1]] = C[1];
    for(i = 2; i <= G; ++i)
    {
        for(j=1;j<=W;j++)
        {
            dp[i][j] = dp[i-1][j];
            if(j>=E[i])
                dp[i][j] = min(dp[i][j],dp[i-1][j-E[i]]+C[i]);
            else dp[i][j] = min(dp[i][j],C[i]);
        }
    }
    if(dp[G][W]!=inf) fout<<dp[G][W]<<"\n";
    else fout<<"-1\n";
    return 0;
}