I have a matrix:

$$A = \begin{pmatrix}
 1 & 1 & 1 & \cdots & 1\\
 0 & 1 & 1 & \cdots & 1\\
 0 & 0 & 1 & \cdots & 1\\
 \vdots & \vdots & \vdots & \ddots & \vdots\\
 0 & 0 & 0 & \cdots & 1 
\end{pmatrix}$$

I need to find $A^{-1}$. How could I do that, knowing that matrix A has size $n \times n$?