Number of PDP#4435
Determine the number of valid bracket sequences of length (consisting of opening and closing brackets), using both round and square brackets, such that no square brackets are nested inside any pair of round brackets.
The input consists of a single line containing a non-negative integer , where 0 \leq n \leq 1000.
Print the remainder when the number of valid bracket sequences is divided by 10^9 + 7.
Example 1