Program Energii;
var G,W : integer;
    EG,CG : array[1..1000] of integer;
    E,C : array[1..1000] of longint;
    rap : array[1..1000] of real;
    Cmin : longint;

procedure Citeste;
var Intrare : text;
    i : integer;
begin
  assign(Intrare,'energii.in');
  reset(Intrare);
  readln(Intrare,G);
  readln(Intrare,W);
  for i:=1 to G do readln(Intrare,EG[i],CG[i]);
  close(Intrare);
end;

procedure Update(ng,en,cost : integer);
begin
  if (en>=W) then
   begin
     if (E[ng]<W) or ((E[ng]>=W) and (C[ng]<cost)) then
      begin
        E[ng]:=en;
        C[ng]:=cost;
        rap[ng]:=cost/en;
      end;
   end
   else
   if (E[ng]<W) and (cost/en<rap[ng]) then
   begin
     E[ng]:=en;
     C[ng]:=cost;
     rap[ng]:=cost/en;
   end;
end;

procedure Calculeaza;
var i,j : integer;
begin
  Cmin:=maxlongint;
  for i:=1 to G do
   begin
     E[i]:=1;
     C[i]:=maxlongint;
     rap[i]:=maxlongint;
   end;
  for i:=1 to G do
   begin
     Update(1,EG[i],CG[i]);
     for j:=1 to i-1 do Update(j+1,E[j]+EG[i],C[j]+CG[i]);
   end;
  for i:=1 to G do
   if E[i]>=W then
    if C[i]<Cmin then Cmin:=C[i];
end;

procedure Scrie;
var Iesire : text;
begin
  assign(Iesire,'energii.out');
  rewrite(Iesire);
  if Cmin<maxlongint then write(Iesire,Cmin)
   else write(Iesire,-1);
  close(Iesire);
end;

begin
  Citeste;
  Calculeaza;
  Scrie;
end.