Guess the number

Chef is playing a game with his brother Chefu. He asked Chefu to choose a positive integer $N$, multiply it by a given integer $A$, then choose a divisor of $N$ (possibly $N$ itself) and add it to the product. Let's denote the resulting integer by $M$; more formally, $M = A \cdot N + d$, where $d$ is some divisor of $N$. Chefu told Chef the value of $M$ and now, Chef should guess $N$. Help him