#include <fstream>
#include <stdio.h>
unsigned long mat[5002][5002];
unsigned long minim(unsigned long a,unsigned long b)
{
    if(a>b) return a;
    else return b;
}
int main()
{
    unsigned long n,w,a[20001],b[20001],inf=99999,i,j;
    FILE*f;
    f=fopen("energii.in","r");
    fscanf(f,"%lu%lu",&n,&w);
    for(i=1;i<=n;i++)
        fscanf(f,"%lu%lu",&a[i],&b[i]);
    fclose(f);
    for(i=0;i<=n;i++)
        for(j=1;j<=w;j++)
            mat[i][j]=inf;
    for(i=1;i<=n;i++)
        for(j=1;j<=w;j++)
            if(a[i]<=j) mat[i][j]=minim(b[i]+mat[i-1][j-a[i]],mat[i-1][j]);
                else mat[i][j]=minim(b[i],mat[i-1][j]);
    FILE*g;
    g=fopen("energii.out","w");
    if(mat[n][w]!=inf) fprintf(g,"%lu",mat[n][w]);
        else fprintf(g,"%d",-1);
    fclose(g);
 return 0;
}