linear algebra - Calculate $lvert A rvert$ if $a_{ij}=0$ if $i=j$ and $1$ otherwise

Let $n$ be a positive integer and let $A=[a_{ij}] \in M_{n\times n} (R)$ be the matrix defined by

$a_{ij}=0$ if $i=j$
$1$ otherwise

To be honest, I've only calculated determinants of matrices with numbers, nothing like this.