45545

uses compl;

const eps = 0.00001;

var z, x, y, p, s: complex;
    k: integer;

begin
    zero(s);
    one(p);
    input(z);
    while(moduz(p) >= eps) do
    begin
        inc(k);
        prod(1/k,z,x);
        prod((2*k-1)/(2*k-3),x,y);
        mult(p,y,p);
        add(s,p,s);
    end;
    output(s);
    writeln
end.