program p1;
var f1,f2:text;
    p,n,x,nr0:longint;
BEGIN
 assign(f1,'fact.in'); reset(f1);
 assign(f2,'fact.out'); rewrite(f2);

  read(f1,p);  x:=1; n:=1;

  while nr0<p do
   begin
    inc(n); x:=x*n;
    while x mod 10=0 do
     begin
      x:=x div 10;
      inc(nr0);
     end;
    if x>100 then x:=x mod 100;
   end;

  if nr0=p then write(f2,n)
           else write(f2,'-1');

 close(f1); close(f2);
END.