program fractorial;
var p,p1,i,x,n:longint;
		f,g:text;
begin
assign (f,'fact.in');
assign (g,'fact.out');
reset (f);
rewrite (g);
read (f,p);
if p=0 then
	n:=1
	else
  begin
	n:=5*p;
for i:=1 to 5 do
begin
x:=5;
p1:=0;
repeat
p1:=p1+trunc(n/x);
x:=x*5
until x>n;
if p1>p then
	n:=n-1
  else
  if p1<p then
  n:=n+1;
if n mod 5<>0 then n:=n-1;
end;
end;
if p1<>p then n:=-1;
write (g,n);
close (f);
close (g)
end.