#include <fstream>
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
const int NMAX = 10001;
int op[NMAX], g, w, e, c, s;
int main() {
   fin >> g >> w;
   for(int i = 0; i <= w; ++i)
       op[i] = NMAX;
   for(int i = 1; i <= g; ++i) {
       fin >> e >> c;
       for(int j = w; j >= 1; --j)
           e >= j ? op[j] = min(op[j], c) : op[j] = min(op[j], op[j - e] + c);
   }
   op[w] == NMAX ? fout << -1 : fout << op[w];
}