KöMaL 2024 A869

Let $A$ and $B$ be given real numbers. Let the sum of real numbers $0\le x_1\le x_2\le\dots\le x_n$ be $A$, and let the sum of real numbers $0\le y_1\le y_2\le\dots\le y_n$ be $B$. Find the largest possible value of ${\sum_{i=1}^n (x_i-y_i)^2}$.