var s:array[1..30] of byte;
    n,i,t:longint;
begin
 read(n);i:=9;t:=31;
 if n=0 then
  begin writeln('10');halt;end
  else if n=1 then begin writeln('1');halt;end;
 while i<>1 do
 begin
  while n mod i=0 do
  begin
   dec(t);
   s[t]:=i;
   n:=n div i;
  end;
  dec(i);
 end;
 if n=1 then
 begin
  for i:=t to 30 do write(s[i]);
  writeln;
 end
  else writeln('?');
end.

I think you should output '-1' instead of '?' if the test has no
solution.

Good luck.

Thank you very much.