#include <cstdio>
#include <algorithm>
#include <iostream>
using namespace std;

int g;
int w;
int e[1005];
int c[1005];
int dp[1005][5005];

int main()
{
	int g,w;
	freopen("energii.in","r", stdin);
	freopen("energii.out","w", stdout);
	scanf("%d %d",&g,&w);
	for(int i=1;i<=g;i++)
		scanf("%d %d",&e[i],&c[i]);
	for(int i=0;i<=g;i++)
		for(int j=0;j<=w;j++)
			dp[i][j]=1<<30; 
	
	for(int i=1;i<=g;i++)
		for(int j=1;j<=w;j++)
		{
			if(j<=e[i])
				dp[i][j]=min(dp[i-1][j],c[i]); 
												
			else
				dp[i][j]=min(dp[i-1][j],dp[i-1][j-e[i]]+c[i]);
		}
		
	if(dp[g][w]==1<<30)
		printf("-1");
	else
		printf("%d",dp[g][w]);
	return 0;
}