for _ in range(int(input())):
    N,S = input().split()
    N = int(N)
    ret = "X"
    if "ooo" in S:
        ret = "O"
    elif "oo-" in S:
        ret = "O"
    elif "o-o" in S:
        ret = "O"
    elif "-oo" in S:
        ret = "O"
    elif "--o-" in S:
        ret = "O"
    elif "-o--" in S:
        ret = "O"
    else:
        f = 0
        for i in range(N):
            if f == 0:
                if S[i] == "o":
                    f = 1
                    cnt = 0
            elif f == 1:
                if S[i] == "-":
                    cnt += 1
                elif S[i] == "o":
                    if cnt % 2 == 1:
                        ret = "O"
                        f = 2
                    else:
                        f = 0
                else:
                    f = 0
            else:
                break
    print(ret)