#include <iostream>
#include <fstream>
//#include <algorithm>

std::ifstream fin("energii.in");
std::ofstream fout("energii.out");

int w, g, ei, ci, v[5005];

int main(int argc, char *argv[])
{
    fin >> g >> w;
    for (int i = 1; i <= w; i++)
        v[i] = 10003;
    for (int contor = 1; contor <= g; contor++)
    {
        fin >> ei >> ci;
        for (int i = w; i >= 0; i--)
            if (ci + v[i] <= v[std::min(w, i + ei)])
                v[std::min(w, i + ei)] = ci + v[i];
    }
    if (v[w] != 10003)
        fout << v[w];
    else
        fout << -1;
    return 0;
}