#include <fstream>
#include <vector>
#include <algorithm>
#define MAXN 1002
#define INF 1<<30
using namespace std;

int main()
{
	bool cont = true;
	int nrGeneratoare, requiredEnergy, energy[MAXN], cost[MAXN], i, j, maxe = 0, **d = new int*[MAXN];
//	vector<vector<int>> d;
	//d.resize(MAXN);
	ifstream f("energii.in");
	ofstream g("energii.out");
	f >> nrGeneratoare >> requiredEnergy;
	//d[0].resize(MAXN);
	d[0] = new int[5005];
	for (i = 1; i <= nrGeneratoare; i++)
	{
		d[i] = new int[5005];
		//d[i].resize(MAXN);
		f >> energy[i] >> cost[i];
		maxe += energy[i];
	}
	f.close();

	if (maxe < requiredEnergy)
	{
		g << -1;
		return 0;
	}
	for (i = 0; i <= nrGeneratoare; i++)
	{
		for (j = 0; j <= requiredEnergy; j++)
		{
			if (i == 0 || j == 0)
			{
				d[i][j] = INF;
			}
			if (i == 1)
			{
				if (energy[i] >= j)
				{
					d[i][j] = cost[i];
				}
				else
				{
					d[i][j] = INF;
				}
			}
		}
	}
	for (i = 2; i <= nrGeneratoare; i++)
	{
		for (j = 1; j <= requiredEnergy; j++)
		{
				if (energy[i] < j)
				{
					d[i][j] = min(d[i - 1][j], d[i - 1][j - energy[i]] + cost[i]);
				}
				else
				{
					d[i][j] = min(d[i - 1][j], cost[i]);
				}
			
		}
	}
	
	g << d[nrGeneratoare][requiredEnergy];
	g.close();
	return 0;
}