#include<fstream>
#include<string.h>
#include<ctype.h>
#include<iostream>
#include<algorithm>
#include<map>
#include<unordered_map>
#include<array>
#include<deque>
#include<unordered_set>
#include<set>
#include<math.h>
using namespace std;
int G, W, dp1[5050], dp2[5050], i, j, eg, cg, cgs, egs,pg,sir=0;
int main()
{
	ifstream f("energii.in");
	ofstream g("energii.out");
	f >> G;
	f >> W;
	pg = 1;
	for (i = 1; i <= G; i++)
	{
		f >> eg >> cg;
		if (eg<=5000)
		{
			if (sir)
			{
				cgs += cg;
				if (cg < pg)
					pg = cg;
				for (j = pg; j <= cgs; j++)
				{
					dp2[j] = max(dp2[j - 1], dp1[j]);
					if (j >= cg)
						dp2[j] = max(dp2[j], dp1[j - cg] + eg);
				}
			}
			else
			{
				cgs += cg;
				if (cg < pg)
					pg = cg;
				for (j = pg; j <= cgs; j++)
				{
					dp1[j] = max(dp1[j - 1], dp2[j]);
					if (j >= cg)
						dp1[j] = max(dp1[j], dp2[j - cg] + eg);
				}
			}
			sir = 1 - sir;
		}
	}
	if (G % 2 == 1)
	{
		for (i = 0; i <= cgs; i++)
			if (dp1[i] >= W)
			{
				g << i;
				return 0;
			}
	}
	else
	{
		for (i = 0; i <= cgs; i++)
			if (dp2[i] >= W)
			{
				g << i;
				return 0;
			}
	}
	g << -1;
	return 0;
}