Twos and Zeros

Kulyash has given you a bag with $(N + M)$ balls having **distinct** colours. Among these, $N$ balls have the number $2$ printed on them and $M$ balls have the number $0$ printed on them. He defines the *score* of a **non-empty** subset $S$ of these $(N + M)$ balls as: $($sum of the balls in $S)$ $-$ $($size of $S)$. Find the count of non-empty subsets of these $(N + M)$ balls having their *s