R.QNBINOM(p,n,psuc,lower_tail,log_p)
p: probability
n: the number of trials
psuc: the probability of success in each trial
lower_tail: if true (the default), the lower tail of the distribution is considered
log_p: if true, log of the probability is used
This function returns the probability quantile function, i.e., the inverse of the cumulative distribution function, of the negative binomial distribution.