
Given a sequence A consisting of n 1s and n 1s, if the sequence A satisfies S (i, A)> = 0 (1 <= i <= 2n) (S (i, X) represents the previous sequence X i term sum), then call it sequence B, given the integer n, find the number of sequences B that satisfy the condition.
Given an integer n (2 <= n <= 3000), find the number of sequences B that meet the above requirements 
