T = int(input())
for _ in range(T):
    N, S = input().split()
    N = int(N)
    dash_count = S.count('-')
    m = dash_count // 2
    found = False
    for i in range(N - 2):
        triplet = S[i:i+3]
        existing_o = triplet.count('o')
        empty_in_triplet = triplet.count('-')
        possible_o = min(empty_in_triplet, m)
        if existing_o + possible_o >= 3:
            print("O")
            found = True
            break
    if not found:
        print("X")