#include <cstdio>

#define GM 1010
#define WM 5010
#define inf 2000000000

long a[WM];
int v[WM], c[WM];
int g, w;

int main()
{
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);

    scanf("%d", &g);
    scanf("%d", &w);

    for (int i=1; i<=g; ++i)
	scanf("%d%d", &v[i], &c[i]);
    for (int i=1; i<=w; ++i)
	a[i]=inf;
    a[0]=0;
	
    for (int i=1; i<=w; ++i)
	for (int j=1; j<=g; ++j)
	    if (i-v[j]>=0)
		if (a[i]>a[i-v[j]])
		    a[i]=a[i-v[j]]+c[j];

    if (a[w]==inf) printf("-1");
    else printf("%ld", a[w]);

    fclose(stdin);
    fclose(stdout);

    return 0;
}