#include<iostream>
#include<fstream>
#define inf 2e8
using namespace std;
int e[1012],cost[1012],cmin=-1;
int a[2][5013],C;
int main(void)
{
	
	
	int n,c;
	fstream f,g;
	f.open("energii.in",ios::in);
	g.open("energii.out",ios::out);
	f>>n>>C;
	int i,maxim=-1;
	for(i=1;i<=n;i++)
	{
		f>>e[i]>>cost[i];
	//	maxim=max(maxim,cost[i]);
	}
	int j;
	for (i=0;i<=1;i++)
		for (j=1;j<=5012;j++)
			a[i][j]=inf;
	for (i=1;i<=n;i++)
		if (i%2==1)
			for (c=1;c<=C;c++)
			{
				if (e[i]<=c)
					a[1][c]=min(a[0][c],a[0][c-e[i]]+cost[i]);
				else
					a[1][c]=min(a[0][c],cost[i]);
			}
		else		
			for (c=1;c<=C;c++)
			{
				if (e[i]<=c)
					a[0][c]=min(a[1][c],a[1][c-e[i]]+cost[i]);
				else
					a[0][c]=min(a[1][c],cost[i]);
			}
		/*
		for(i=1;i<=n;i++)
			for(j=1;j<=C;j++)
			{
				if(e[i]<=j)
					a[i][j]=min(a[i-1][j],a[i-1][j-e[i]]+cost[i]);
				else
					a[i][j]=min(a[i-1][j],cost[i]);
			}
		*/
		
	if (a[n%2][C]!=inf)
		g<<a[n%2][C];
	else
		g<<-1;
}