def letter_id(c):
    return ord(c)-ord('A')

def rest(freq):
    ans = []
    for i in range(26):
        if freq[i] > 0:
            ans.append((chr(ord('A') + i)) * freq[i])
    return ''.join(ans)

def get_word(prev, freq):
    if len(prev) == 0:
        return rest(freq)
    prev_c = prev[0]
    if freq[letter_id(prev_c)] > 0:
        freq[letter_id(prev_c)] -= 1
        result = get_word(prev[1:], freq)
        freq[letter_id(prev_c)] += 1
        if result is not None:
            return prev_c + result
    for i in range(letter_id(prev_c)+1, 26):
        if freq[i] > 0:
            freq[i] -= 1
            return chr(ord('A') + i) + rest(freq)
    return None

def work_try(x):
    prev = ''
    for word in x:
        freq = [0] * 26
        for c in word:
            freq[letter_id(c)] += 1
        new_word = get_word(prev, freq)
        if new_word is None:
            return False
        prev = new_word
    return True

def work(n, x):
    if n == 2:
        for i in range(1, len(x)-1):
            candidate = [x[:i], x[i:]]
            if not work_try(candidate):
                return candidate
    else:
        for i in range(1, len(x)):
            for j in range(i+1, len(x)):
                candidate = [x[:i], x[i:j], x[j:]]
                if not work_try(candidate):
                    return candidate
    return None
    
tt = int(input().strip())
for t in range(1, tt+1):
    ns, bb = input().strip().split()
    nn = int(ns)
    ans = work(nn, bb)
    if ans is None:
        print('Case #%d: IMPOSSIBLE' % t)
    else:
        print('Case #%d: POSSIBLE' % t)
        print(' '.join(ans))