#include <stdio.h>
#include <stdlib.h>

const int maxsize = 10001;

int ee[maxsize];
int cg[maxsize];
int a[maxsize];
int poz[maxsize];

bool in(int k, int s)
{
	if(s <= 0 )
		return false;
	int m = s;
	int ss = poz[m];
	while(ss != -1)
	{
		if(ss == k)
			return true;
		m = m-ee[poz[m]];
		ss = poz[m];
	}
	return false;
}

int main(void)
{
	FILE *fin;
	FILE* fout;
	fin = fopen("energii.in", "r");
	fout = fopen("energii.out", "w");
	int g;
	int w;
	fscanf(fin, "%d\n", &g);
	fscanf(fin, "%d\n", &w);
	int i=0;
	int total = 0;
	for(;i<g;++i)
	{
		int ee1, cg1;
		fscanf(fin, "%d %d\n", &ee1, &cg1);
		ee[i] = ee1;
		cg[i] = cg1;
		total += ee1;
	}
	fclose(fin);

	bool found = false;
	a[0] = 0;
	for(int k=0;k<g;++k)
	{
		if(cg[k] == 0)
			a[0] += ee[k];
	}

	if(a[0] >= w)
	{
		fprintf(fout, "0\n");
		fclose(fout);
		return 0;
	}

	if(total < w) 
	{
		fprintf(fout, "-1\n");
		fclose(fout);
		return 0;
	}
	
	a[0] = 0;
	poz[0] = -1;
	int min = 1001*10002;
	for(i=1;i<=maxsize;++i)
	{
		int pozm = -1;
		a[i] = 1001*10002;
		for(int k=0;k<g;++k)
		{
			if(ee[k] <= i && !in(k, i-ee[k])) 
			{
					if(cg[k] + a[i-ee[k]] < a[i])
					{
						a[i] = cg[k] + a[i-ee[k]];
						pozm = k;
					}
			}
		}
		poz[i] = pozm;
		if(i >= w && min > a[i])
			min = a[i];
	}
	
	for(int k=0;k<g;++k) 
	{
		if(ee[k] > w && ee[k] < 100002) 
		{
			if(cg[k] < min)
				min = cg[k];
		}
	}

	fprintf(fout, "%d\n", min);
	fclose(fout);
	return 0;
}