program factorial;
var p,c,f:longint;
    n:int64;
    i,o:text;
begin
  assign(i,'fact.in');
  reset(i);
  read(i,p);
  n:=0;
  repeat
    n:=n+5;
    c:=c+1;
    if c mod 5=0 then
      f:=f+1
  until c+f>=p;
  assign(o,'fact.out');
  rewrite(o);
  if c+f=p then
    write(o,n)
  else
    write(o,'-1');
  close(o);
end.