Mutual Friends

You are given a task to make a simple version of mutual friends finder. There are $N$ people on a social media network. You are provided with a $\textbf{2D matrix}$ whose entry in the $\textbf{i}^{th}$ row and $\textbf{j}^{th}$ column represents whether person $\textbf{i}$ and person $\textbf{j}$ are friends (value = 1) or not friends (value = 0). Note that every person is a friend of himself