var n:longint;
    s,ss:string;
    i:integer;
begin
readln(n);s:='';
i:=9;
if n=1 then write('1') else
if n=0 then write('10') else begin
while i>1 do begin
if n mod i=0 then begin str(i,ss);s:=s+ss;n:=n div i;end
else dec(i);
end;

if ss='' then write('-1')
else for i:=length(s) downto 1 do write(s[i]);

end;
end.

Easy program IMHO but WA at test10-Why?

How about example with n=22? Your program will write 2, but 22 is not a 2! :) You must check n in the end of loop for equal 1. Your program can't work if n include prime devisor more than 7. It's easy. My problem was test 4 ;)