def solve(N, S):
    for i in range(N - 2):
        if S[i:i + 3] in ('ooo', 'o-o', '-oo', 'oo-'):
            return True
    return False


T = int(input())
for _ in range(T):
    N, S = input().split()
    N = int(N)
    print('O' if solve(N, S) else 'X')