program fractorial;
var p,p1,i,x,n:longint;
		f,g:text;
    gata:boolean;
begin
assign (f,'fact.in');

reset (f);
read (f,p);
close (f);
if p=0 then
	n:=1
else
  begin
	n:=4*p+1;
	gata:=false;
  repeat
		x:=5;
		p1:=0;
		repeat
			p1:=p1+trunc(n/x);
			x:=x*5
		until x>n;
		if p1>=p then
  		gata:=true
  	else
  		n:=n+1;
  until gata;
	if p1<>p then
		n:=-1;
  end;
assign (g,'fact.out');
rewrite (g);
write (g,n);
close (g)
end.