#include <fstream>
#include <algorithm>

using namespace std;
int D[5003], E[1010], C[1010],G ,W,sum;
ifstream cin("energii.in");
ofstream cout("energii.out");
int main(){
    cin >> G >> W;
    for (int i = 1; i <= G; i++)
        cin >> E[i] >> C[i];
 
    for (int i = 1; i <= W; i++) D[i] = 1e6;
	for (int i = 1; i <= G; i++) 
		for (int j = W; j >= 1; j--)
			if(j >= E[i])
			D[j] = min(D[j],D[j-E[i]]+C[i]);
			else D[j] = min(D[j],C[i]);
    if(D[W] == 1e6) cout << -1;
           else cout<<D[W];
return 0;
}