program L6_3;
uses crt;
var f:text;
    Zna4,k:real;
    n,i:integer;
begin
    assign(f,'input.txt');
    reset(f);
    readln(f,n);
    close(f);


    zna4:=cos(n);
    k:=cos(n);
    if n<>1 then
    begin
    for i:=n downto 2 do
    begin
    zna4:=cos(i-1+k);
    k:=zna4;
    end;
    end;

assign(f,'output.txt');
rewrite(f);
writeln(f,Zna4:8:6);
close(f);
end.