t = int(input())
for _ in range(t):
    n,s = input().split()
    n = int(n)
    cand = ''
    for c in s:
        if c=='x':
            cand = ''
            continue
        cand += c
        if cand[-3:] in ('ooo','oo-','-oo','o-o'):
            print('O')
            break
        elif len(cand)==4 and cand in ('--o-', '-o--'):
            print('O')
            break
        elif len(cand)==4:
            cand = cand[1:]
    else:
        print('X')