program my;
uses crt;
var t,x:real; k,m:integer;
begin readln(x);
k:=1; t:=0;
repeat
t:=t+((sin(x)/cos(x)+k)/2*k*x);
k:=k+1
until abs((sin(x)/cos(x)+k)/2*k*x)>=m;
writeln('t=',t:10:5);
readln;
end.