n=int(input())
a="impossible"
for i in range(n):
	c=0
	s=input()
	if 'W' in s[-2:]: c-=1
	else:
		s=s.replace('W','')
		for x in s:
			if x=='G':c+=1
			else:c-=1
			if c<0: break
	print(a[(c==0)*2:])