for _ in range(int(input())):
    w = g = 0
    b = r = True
    for c in input():
        r = False
        if c == 'W':
            w += 1
            b = False
        elif c == 'G':
            if w == 0:
                break
            w -= 1
            g += 1
            b = True
        elif g != 0:
            r = True
            g -= 1
    if r and b:
        print('possible')
    else:
        print('impossible')