import sys
input = sys.stdin.readline

def solve(S):
    if "ooo" in S or "-oo" in S or "oo-" in S:
        print("O")
        return 
    pre = -1
    for i in range(int(N)):
        if S[i] == "x":
            pre = -1
        elif S[i] == "o":
            if pre != -1 and (i - pre) % 2 == 0:
                print("O")
                return
            pre = i
    print("X")

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