def determine_winner(n, s):
    # Check if current s has three consecutive 'o's
    if has_three_o(s):
        return "O"
    
    # Check if O can win in the next move
    for i in range(n):
        if s[i] == '-':
            # Check three possible patterns
            # Pattern 1: left two are 'o's
            if i >= 2 and s[i-2] == 'o' and s[i-1] == 'o':
                return "O"
            # Pattern 2: left and right are 'o's
            if i >= 1 and i < n-1 and s[i-1] == 'o' and s[i+1] == 'o':
                return "O"
            # Pattern 3: right two are 'o's
            if i <= n-3 and s[i+1] == 'o' and s[i+2] == 'o':
                return "O"
    
    # If none of the above, X wins
    return "X"

def has_three_o(s):
    for i in range(len(s) - 2):
        if s[i] == 'o' and s[i+1] == 'o' and s[i+2] == 'o':
            return True
    return False

t = int(input())
for _ in range(t):
    n, s = input().split()
    n = int(n)
    print(determine_winner(n, s))