You are given a string (T) of length (n) ( (n) is even ), which consists of ' a ', ' b ', and ' ? '. Please count the strings (S) which satisfy the following conditions: (|S|=n); (S_i) is either ' a ' or ' b ' for all (1 \le i \le n); (S_i=T_i) for all (1 \le i \le n) such that (T_i) is not ' ? '; There exist two (possibly empty) strings (A) and (B) such that (S=A+B+B+A). Here, (+) denotes string concatenation . As the answer may be inexplicably huge, you are only asked to compute it modulo (998\,244\,353). Each test contains multiple test cases. The first line contains the number of test cases (t) ((1 \le t \le 10^4)). The description of the test cases follows. The first line of each test case contains a single integer (n) ((2 \le n \le 400\,000), (n) is even ). The second line of each test case contains a string (T) of length (n), consisting of ' a ', ' b ', and ' ? '. It is guaranteed that the sum of (n) over all test cases does not exceed (400\,000). For each test case, output the answer modulo (998\,244\,353) on a separate line. For the fifth test case, there are (10) corresponding strings which are as follows: " aaaabaaaaaba " " aaaabbaaabba " " aaabbaaaabba " " aaabbbaabbba " " abaabbbaabba " " ababbbbabbba " " baaabaaababa " " baaababaaaba " " baaabbaabbba " " baabbabaabba "