write a go solution for Description:
You are given a sequence A, where its elements are either in the form + x or -, where x is an integer.

For such a sequence S where its elements are either in the form + x or -, define f(S) as follows:

- iterate through S's elements from the first one to the last one, and maintain a multiset T as you iterate through it.
- for each element, if it's in the form + x, add x to T; otherwise, erase the smallest element from T (if T is empty, do nothing).
- after iterating through all S's elements, compute the sum of all elements in T. f(S) is defined as the sum.

The sequence b is a subsequence of the sequence a if b can be derived from a by removing zero or more elements without changing the order of the remaining elements. For all A's subsequences B, compute the sum of f(B), modulo 998,244,353.

Input Format:
The first line contains an integer n (1<=n<=500) — the length of A.

Each of the next n lines begins with an operator + or -. If the operator is +, then it's followed by an integer x (1<=x<998,244,353). The i-th line of those n lines describes the i-th element in A.

Output Format:
Print one integer, which is the answer to the problem, modulo 998,244,353.

Note:
In the first example, the following are all possible pairs of B and f(B):

- B= {}, f(B)=0.
- B= {-}, f(B)=0.
- B= {+ 1, -}, f(B)=0.
- B= {-, + 1, -}, f(B)=0.
- B= {+ 2, -}, f(B)=0.
- B= {-, + 2, -}, f(B)=0.
- B= {-}, f(B)=0.
- B= {-, -}, f(B)=0.
- B= {+ 1, + 2}, f(B)=3.
- B= {+ 1, + 2, -}, f(B)=2.
- B= {-, + 1, + 2}, f(B)=3.
- B= {-, + 1, + 2, -}, f(B)=2.
- B= {-, + 1}, f(B)=1.
- B= {+ 1}, f(B)=1.
- B= {-, + 2}, f(B)=2.
- B= {+ 2}, f(B)=2.

The sum of these values is 16.. Output only the code with no comments, explanation, or additional text.