{-------------------------------

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  # Max Tkachenko # Group 112 #
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}

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*x / c / (c+1);
         y := y + a;
         c := c+2
       end;
 
     writeln(y)
 end.