Model of Poison regression

model.stan

data {
  int<lower=0> N;
  real x[N];
  real f[N];
  int<lower=0,upper=100> y[N];
}
parameters {
  real b0;
  real b1;
  real b2;
}
model {
  for (n in 1:N) 
      log(y[n]) ~ poisson(b0 + x[n]* b1 + f[n] * b2);
}