#include <iostream>
#include <fstream>
#include <cstring>
#define NMAX 1010
using namespace std;

ifstream f("energii.in");
ofstream g("energii.out");

int a[NMAX][NMAX] ;
int e[NMAX],c[NMAX];
int emin,n;
//          unsolved
int main()
{
    f >> n >> emin;
    for(int i=1; i<=n; i++)
    {
        f >> e[i] >> c[i];
    }

    for(int i=0;i<=n;i++)
        for(int j=1;j<=emin;j++)
                a[i][j] = 10000000;

    for(int i=1;i<=n;i++){
        for(int w=1;w<=emin;w++){
            a[i][w] = a[i-1][w];
            if(w >= e[i])      a[i][w] = min(a[i][w],a[i-1][w-e[i]] + c[i]);
            else if(w <= e[i]) a[i][w] = min(a[i][w],c[i]);
        }
    }
    if(a[n][emin] == 10000000) g << -1;
    else g << a[n][emin];
    return 0;
}