program factorial;
var
  n, p, i: longint;
  f: text;

Function Nulla(x: longint): longint;
var o, r: longint;
begin
  o := 5; r := 0;

  While x div o <> 0 do
    begin
      r := r + x div o;
      o := o * 5;
    end;
  Nulla := r;
end;

Begin
  Assign(f, 'fact.in');
  Reset(f);
  ReadLn(f, p);
  Close(f);
  for i := 1 to 1000000 do
    if Nulla(i) = p then
      begin
        n := i;
        Break;
      end;
  WriteLn(n);
end.