program curentelele;

var
    g,w,i,n,aux:integer;
    f:text;
    eg,cg:array[1..1001] of integer;

begin
 assign(f,'energii.in');
 reset(f);
 readln(f,g);
 readln(f,w);
 for i:=1 to g do readln(f,eg[i],cg[i]);
 close(f);

 for i:=1 to g-1 do if (eg[i]<eg[i+1]) or ((eg[i]=eg[i+1]) and (cg[i]>cg[i+1])) then begin
                                                                                    aux:=eg[i];
                                                                                    eg[i]:=eg[i+1];
                                                                                    eg[i+1]:=aux;
                                                                                    aux:=cg[i];
                                                                                    cg[i]:=cg[i+1];
                                                                                    cg[i+1]:=aux;
                                                                                    end;
 i:=1;
 aux:=0;
 repeat
  n:=eg[i]+n;
  aux:=cg[i]+aux;
  i:=i+1;
 until (n>=w) or (i>g);
 assign(f,'energii.out');
 rewrite(f);
 if n>=w then write(f,aux)
         else write(f,-1);
 close(f);
 end.