var n,m,k,p,i,j:longint;
    f,g:text;
begin
assign(f,'fact.in');
assign(g,'fact.out');
reset(f);
rewrite(g);
read(f,p);
if p=0 then write(g,1) else
begin
  i:=p;
  m:=0;
  while i>0 do
   begin
    m:=m+5;
    n:=m;
    repeat
      k:=k+1;
      n:=n div 5;
    until n mod 5 <>0;
    i:=i-k;
    k:=0;
   end;
 if i<0 then write(g,-1) else
   write(g,m);
end;
close(f);
close(g);
end.