import sys
def input(): return sys.stdin.readline().strip()
def mapint(): return list(map(int, input().split()))
sys.setrecursionlimit(10**9)

T = int(input())
def check(S):
    vic = 0
    vic_prob = set()
    length = len(S)
    for i in range(length-2):
        s = ''.join(S[i:i+3])
        if s=='ooo':
            vic += 1
        elif s=='oo-' or s=='-oo' or s=='o-o':
            vic_prob.add(i+('-oo', 'o-o', 'oo-').index(s))
    cnt = 0
    o = False
    for i in range(length):
        if S[i]=='o':
            o = True
            if cnt % 2==1:
                vic += 1
            cnt = 0
        elif S[i]=='x':
            o = False
            cnt = 0
        else:
            if o:
                cnt += 1
    
    if length>=4:
        for i in range(length-3):
            s = ''.join(S[i:i+4])
            if s=='--o-' or s=='-o--':
                vic += 1
    return vic, len(vic_prob)
        
        

for _ in range(T):
    N, S = input().split()
    N = int(N)
    S = list(S)
    if N<3:
        print('X')
        continue
    v, p = check(S)
    if v>0 or p>0:
        print('O')
        continue
    else:
        print('X')