Log likelihood function for binary classification

Question

I need help with this following task. There is a binary classification problem where each observation xn is belong to one of two classes ($t = 0$ and $t = 1$). The training data points are sometimes mislabeled. For every data point $x_n$, instead of having a value $t$ for the class label, we have a value $\pi_n$ representing the probability that $t_n = 1$. Given a probabilistic model $p(t = 1_\varphi)$ what is the log likelihood function?