program factorial;
var p,c,v,i: integer;
 f,g:text;
begin
assign(f, 'fact.in');
reset(f);
assign(g, 'fact.out');
 rewrite(g);

  readln(f,p);
  close(f);
  i:=5;
  c:=1;
  if(p=0) then  writeln(-1) else
  begin
       while(c<>p) do
       begin
          i:=i+1;
          v:=I;
       
               while(v mod 5 = 0) do
               begin
                c:=c+1;
                v:=v div 5;
               end;
       end;
  end;
  writeln(g, i);
  close(g);

end.