linear algebra - Find the eigenvalues of a matrix with ones in the diagonal, and all the other elements equal

Let $A$ be a real $n\times n$ matrix, with ones in the diagonal, and all of the other elements equal to $r$ with $0

How can I prove that the eigenvalues of $A$ are $1+(n-1)r$ and $1-r$,
with multiplicity $n-1$?