program factorial;
var p,n,f,c:longint;
    i,o:text;
begin
  assign(i,'factorial.in');
  assign(o,'factorial.out');
  reset(i);
  rewrite(o);
  read(i,p);
  c:=p;
  f:=0;
  repeat
    c:=c div 5;
    inc(f)
  until c=0;
  n:=5*(p-f+1);
  if p=0 then
    write (o,'1')
  else
    write(o,n);
  close(o)
end.