def determine_winner(N, S):
    # 检查是否存在三个连续的o
    for i in range(N - 2):
        if S[i] == 'o' and S[i+1] == 'o' and S[i+2] == 'o':
            return "O"
    
    # 检查是否存在三个连续的位置，其中至少有两个o和一个-
    for i in range(N - 2):
        triplet = [S[i], S[i+1], S[i+2]]
        count_o = triplet.count('o')
        has_minus = '-' in triplet
        if count_o >= 2 and has_minus:
            return "O"
    
    # 其他情况X赢
    return "X"

T = int(input())
for _ in range(T):
    N, S = input().split()
    N = int(N)
    print(determine_winner(N, S))