program numere;
var v,s,c:array[1..700] of integer;
    i,j,lmin,n,d:integer;
    f,g:text;

begin
assign(f,'energii.in');
reset(f);
assign(g,'energii.out');
rewrite(g);
readln(f,n);
readln(f,d);
for i:=1 to n do
 begin
  readln(f,v[i],c[i]);
  s[i]:=c[i];
 end;
lmin:=s[n];
for i:=n-1 downto 1 do
begin
 for j:=i+1 to n do
 begin
  if (v[i]+v[j]>=d) and (c[i]+c[j]<=v[j]+v[i]) then
  begin
   s[i]:=s[i]+c[j];
   if (s[i]<lmin) then lmin:=s[i];
  end;
 end;
end;
if (lmin<d) then writeln(g,-1)
else
writeln(g,lmin);
close(g);
close(f);
end.