#include <stdio.h>

#define en_MAX 5001

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);
    RG[W] = en_MAX + 1;
    for(k = 1; k <= G; ++k)
    {
        scanf("%d %d",&ce,&cc);
        for(i = mx; i >= 1; --i)
        {
            if(RG[i] > 0){
            if(i + ce < W){
                if((RG[i] + cc < RG[i + ce] || RG[i + ce] == 0) )
                    {
                        RG[i + ce] =  RG[i] + cc;
                        if(i + ce > mx)
                            mx = i + ce;
                    }
            }
            else
                if(i + ce >= W && RG[i] + cc < RG[W])
                    RG[W] = RG[i] + cc;
            }

        }
            if(ce >= W && cc < RG[W])
                RG[W] = cc;
            else
                if(RG[ce] > cc || RG[ce] == 0)
                {
                    RG[ce] = cc;
                    if(ce > mx)
                        mx = ce;
                }
    }
    if(RG[W] == 0)
        printf("-1\n");
    else
        printf("%d\n",RG[W]);
    return 0;
}