#include<cstdio>
#define DN 1001
#define MIN(a,b) ((a)<(b)? (a):(b))
#define LUNG 9999
int main()
{
	FILE *f=fopen("energii.in", "r");
	FILE *g=fopen("energii.out", "w");
	int G, w, eg[1001], cg[1001], i, j, a[DN][DN], tot;
	fscanf(f, "%d %d", &G, &w);
	for(i=1; i<=G; i++)
	{
		fscanf(f, "%d %d", &eg[i], &cg[i]);
		tot=tot+eg[i];
	}
	if(tot<w)
	{
		fprintf(g, "-1");
		return 0;
	}
	for(j=1; j<=w; j++)
		a[0][j]=LUNG;
	for(i=1; i<=G; i++)
		for(j=1; j<=w; j++)
		{
			if(j<eg[i])
				a[i][j]=MIN(a[i-1][j], cg[i]);
			else
				a[i][j]=MIN(a[i-1][j], a[i-1][j-eg[i]]+cg[i]);
		}
	fprintf(g, "%d", a[G][w]);
	return 0;
}