{-------------------------------
   ... ln x ...
 -------------------------------
  # Max Tkachenko # Group 112 #
 -------------------------------
}

Program task_5_20___B(input,output);

 const eps = 1E-3; 

 var a, x, y : real;
       c : integer;

 begin

   read(x);
    
    c:=2;  

    y:=x;
      a:=y;
    
  while abs(a) >= eps do
    begin 
      a := - a*x / c;
      y := y+1; 
      c := c+1 
    end;

     writeln(y)
 end.