var n,w,x,y,m,i,j:longint;
a:array[1..6005] of longint;
f,g:text;
begin
assign(f,'energii.in');reset(f);
assign(g,'energii.out');rewrite(g);
readln(f,n,w);
m:=maxlongint;
for i:=1 to n do begin
read(f,x,y);
if (x>=w) then begin
if y<m then m:=y;
end
          else begin
          for j:=(m-x) downto m do
          if a[j]+y>m then m:=a[j]+y;
               end;
                 end;
if m>maxlongint then writeln(g,m)
                 else writeln(g,'-1');
close(f);
close(g);
end.