Modulo or Multiply

A function $f(X, Y)$ creates an array $A$ of size $Y$ such that $A[i] = (X*i)\%Y$ and returns the number of unique elements in that array. You are given two integers $M$ and $N$. You have to create another array $B$ of size $N$ such that $B[i] = f(M, M+i)$ where, $1 \leq i \leq N$. Can you tell the maximum size of a prefix subarray of $B$ (subarray starting from $B[1]$) such that its elements are