#include<cstdio>
const int maxN=1001,maxW=5001,I=2000000001;
int g,w,e[maxN],c[maxN],a[maxN][maxW];

int min(int x,int y)
{
	if(x<y)
		return x;
	return y;
}
void read()
{
	int i;
	freopen("energii.in","r",stdin);
	freopen("energii.out","w",stdout);
	scanf("%d",&g);
	scanf("%d",&w);
	for(i=1;i<=g;++i)
		scanf("%d%d",&e[i],&c[i]);
}
void work()
{
	int i,j;
	for(i=0;i<=g;++i)
		for(j=1;j<=w;++j)
			a[i][j]=I;
	for(i=1;i<=g;++i)
		for(j=1;j<=w;++j)
			if(e[i]<=j)
				a[i][j]=min(a[i-1][j],a[i-1][j-e[i]]+c[i]);
			else a[i][j]=min(a[i-1][j],c[i]);
	if(a[g][w]==I) 
		printf("-1\n");
		else printf("%d\n",a[g][w]);
}

int main()
{
	read();
	work();
	return 0;
}