program centrala;
type sir=array[0..1001] of integer;
     matrice=array[0..1001,0..5001] of integer;
var e,c:sir;
    r:matrice;
    g,en,i,j:integer;
    o,d:text;
function min(a,b:integer):integer;
begin
  if a<b then min:=a else min:=b;
end;
begin
assign(d,'energii.in');assign(o,'energii.out');
reset(d);rewrite(o);
read(d,g);
read(d,en);
for i:=1 to g do
  begin
    read(d,e[i]);
    read(d,c[i]);
  end;
for i:=0 to en do r[0,i]:=30000;
for i:=1 to g do r[i,0]:=30000;
for i:=1 to g do
  for j:=1 to en do
    if e[i]>=j then r[i,j]:=min(c[i],r[i-1,j]) else r[i,j]:=min(r[i-1,j],r[i-1,j-e[i]]+c[i]);
if r[i,j]<>30000 then writeln(o,r[i,j]) else writeln(o,-1);
close(d);
close(o);
end.