#include <iostream>
#include <fstream>
#define inf8 2000000000
using namespace std;
ifstream fin("energii.in");
ofstream fout("energii.out");
int dp[10005], e, p, G, W;
int main() {

	fin >> G >> W;
	for(int i = 1; i <= W; i++ )
		dp[i] = inf8;
	for(int i = 1; i <= G; i++)
	{
		fin >> e >> p;
		for(int j = W; j >= 1; j--)
			dp[j] = min(dp[j], dp[j - e] + p);
		for(int j = e; j >= 1; j--)
			dp[j] = min(dp[j], p);
	}
	if(dp[W] != inf8)
		fout << dp[W];
		else fout << -1;
	return 0;
}