def main(): import sys input = sys.stdin.readline for _ in range(int(input())): N, line = input().split() N = int(N) ans = 'X' for i in range(N-2): s = line[i: i+3] if s == 'ooo' or s == 'oo-' or s == 'o-o' or s == '-oo': ans = 'O' for i in range(N-3): s = line[i: i + 4] if s == '-o--' or s == '--o-': ans = 'O' for i in range(N-4): s = line[i: i+5] if s == 'o---o': ans = 'O' print(ans) if __name__ == '__main__': main()