#include <stdio.h>

#define en_MAX 25001

int RG[en_MAX];

int main()
{
    freopen("energii.in","r",stdin);
    freopen("energii.out","w",stdout);
    int G,W,ce,cc,mx = 0,k,i,j;
    scanf("%d\n%d\n",&G,&W);
    for(k = 1; k <= G; ++k)
    {
        scanf("%d %d",&ce,&cc);
        for(i = mx; i >= 1; --i)
        {
            if(i + ce <= en_MAX)
                if(RG[i] > 0 && (RG[i] + cc < RG[i + ce] || RG[i + ce] == 0) )
                    {
                        RG[i + ce] =  RG[i] + cc;
                        if(i + ce > mx)
                            mx = i + ce;
                    }
        }
            if((RG[ce] != 0 && RG[ce] > cc) || RG[ce] == 0)
            {
                RG[ce] = cc;
                if(ce > mx)
                    mx = ce;
            }
    }
    int minim = en_MAX;
    for(k = W; k <= en_MAX; ++k)
    {
        if(RG[k] != 0 && RG[k] < minim)
            minim = RG[k];
    }
    if(minim == en_MAX)
        printf("-1\n");
    else
        printf("%d\n",minim);
    return 0;
}