program p1;
var fi,fo:text;
    total,n,w,i,j,x:integer;
    a:array[1..1010,1..2] of integer;
    t:array[-1..1010,-1..1010]of integer;
    ok:boolean;

procedure citire;
 begin
  read(fi,n,w);
  for i:=1 to n do
   begin
    read(fi,a[i,1],a[i,2]);
    total:=total+a[i,2];
   end;
  if total<w then begin writeln(fo,'-1'); close(fi); close(fo); halt; end;
 end;

BEGIN
 assign(fi,'energii.in'); reset(fi);
 assign(fo,'energii.out'); rewrite(fo);

  citire;
  x:=0;
  while (x<=w)or(t[0,x]=0) do
   begin
    inc(x);
    ok:=true;
    for i:=1 to n do
     if (ok)and(x-a[i,1]>=0)or(x-a[i,1]>=0)and(t[i,x]=0)and(t[0,x-a[i,1]]+a[i,2]<t[0,x]) then
     if (x-a[i,1]=0)or(x-a[i,1]<>0)and(t[0,x-a[i,1]]<>0)then
      begin
       t[0,x]:=t[0,x-a[i,1]]+a[i,2];
       for j:=1 to n do t[j,x]:=t[j,x-a[i,1]];
       t[i,x]:=1;
       ok:=false;
      end;
   end;

  writeln(fo,t[0,x]);

 close(fi); close(fo);
END.