var n,i,j,w,x,y,p,x1:integer;
    f,g:text;
    a:array[0..1001,0..5001]of longint;
begin
assign(f,'energii.in');reset(f);assign(g,'energii.out');rewrite(g);
read(f,n,w);
for i:=1 to n do
  begin
     read(f,x,y);
     p:=1;   x1:=x;
     while x<=w do
       begin
          if i=1 then a[i,x]:=p*y else
             if p*y<a[i-1,x] then a[i,x]:=p*y
                             else a[i,x]:=a[i-1,x];
          x:=x+x1;
          p:=p+1;
       end;
  end;
if a[n,w]<>0 then write(g,a[n,w]) else write(g,-1);
close(f);close(g);
end.