var p, i, n, t:int64;
    f, g:text;
    ok:boolean;


begin
assign (f, 'factorial.in'); reset (f);
assign (g, 'factorial.out'); rewrite (g);

read (f, p);
if p>=0 then
  begin
  i:=1; ok:=true;
  while ok do
    begin
    if i mod 5 = 0 then
      begin
      n:=i;
      while n mod 5 = 0 do
        begin
        t:=t+1;
        n:=n div 5;
        end;
      end;
    if t>=p then ok :=false;
    i:=i+1;
    end;
  writeln (g, i-1);
  end
                else writeln (g, '-1');

close (f); close (g);
end.