my-solutions/codeforces/round-923/task-a/main.cpp

#include <iostream>

using namespace std;

int main() {
    int t;
    cin >> t;
    for (int i = 0; i < t; i++) {
        size_t n;
        cin >> n;

        std::string buffer;
        cin >> buffer;

        int first_b = -1;
        int last_b = -1;

        for (int j = 0; j < n; j++) {
            if (buffer[j] == 'B') {
                if (first_b == -1) {
                    first_b = j;
                }
                last_b = j;
            }
        }

        cout << last_b - first_b + 1 << endl;
    }
}