program ex;
const
  maxn=20;
var
  i,n:longint;
  flag:boolean;
  z:integer;
  a:array[1..maxn]of byte;

function check(x:longint):boolean;
var
  i:longint;
begin
  check:=true;
  for i:=2 to trunc(sqrt(x)) do
    if x mod i=0 then
    begin
      if i>10 then begin writeln(-1); halt; end;
      check:=false;
      exit;
    end;
end;

procedure solve(x:longint);
var
  i:integer;
begin
  if check(x) then
    if x<10 then
    begin
      z:=z+1;
      a[z]:=x;
      exit;
    end
    else
    begin
      writeln(-1);
      halt;
    end;
  for i:=9 downto 2 do
    if x mod i=0 then
    begin
      flag:=false;
      z:=z+1;
      a[z]:=i;
      x:=x div i;
      solve(x);
      break;
    end;
end;

begin
  readln(n);
  flag:=true;
  fillchar(a,sizeof(a),0);
  z:=0;
  if n=0 then writeln(10) else
  if (n>=1) and (n<=9) then writeln(n) else
  begin
    solve(n);
    for i:=z downto 1 do write(a[i]);
  end;
  writeln;
end.

your program prints 1 sometimes..
for example the tests
252 - the answer is 479 you print 1479
72 - the answer is 89 you print 189

good luck.