program kozelites;
uses wincrt;

var s,a,b,alfa,x1,x2,x3,pontossag:real;

function egyenlet (alfa:real):real;
   var x:real;
   begin
    x:=alfa/2-sin(alfa/2)*cos(alfa/2)-1;
    egyenlet:=x;    
   end;

procedure hasonlitas (x1,x2:real ; var x3:real);
  var y:real; 
 begin
  repeat
   x3:=(x1+x2)/2;  Writeln(x3:10:7,egyenlet(x3));
   y:=egyenlet(x3)*egyenlet(x1); 
    if y>0 then                                     {!}
     x1:=x3  else 
    if y<0 then                                     {!}
     x2:=x3;
  until abs(x2-x1)<pontossag;
 end;

begin

pontossag:=1E-6;                                    {!}
a:=0;
b:=pi;
hasonlitas (a,b,x3);
writeln(x3);



end.