Nth Fibonacci Number

//@version=2
study("Nth Fibonacci Number")
//-----------------
//Binet's Formula to solve the Nth Fibonacci Number
f_n_fib(_step) =>
    _phi = 1.618
    _n_phi = 1/_phi
    _return = round(_step >= 0 ? pow(_phi, _step) / sqrt(5) : pow(-_n_phi, _step) / sqrt(5))
//-----------------
step = na(step[1]) ? 1 : n >= f_n_fib(step[1]) ? step[1]+1 : step[1]
current_fib = f_n_fib(step)
plot(title='Fib Time Number', series=current_fib, color=black)