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