#include <fstream>
#include <iostream>
#include <algorithm>
#define NMAX 5010
#define VMAX 1000000
using namespace std;

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

int val[NMAX],b[NMAX];
int main()
{
    int N,W,eg,cg;
    f >> N >> W;
    for(int i = 1; i <= W; i++)
        b[i] = VMAX;
    for(int i = 1; i <= N; i++){
        f >> eg >> cg;
        for(int j = 1; j <= W; j++){
            if(eg >= j)
                val[j] = min(b[j], cg);
            else
                val[j] = min(b[j], b[j-eg] + cg);
        }
        for(int j = 1; j <= W; j++)
            b[j] = val[j];
    }
    if(val[W] == VMAX)
        g << -1;
    else
        g << val[W];
    return 0;
}