#!/usr/bin/env python3
# %%
import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines


# %%
T = int(readline())
query = readlines()

# %%


def solve(q):
    w_min = 0
    w_max = 0
    g = 0
    for a in q.rstrip().decode():
        if a == 'W':
            w_min = 1
            w_max += 1
        elif a == 'G':
            if not w_max:
                return False
            w_min = 0
            w_max -= 1
            g += 1
        else:
            if not g:
                return False
            g -= 1
    return w_min == 0 and g == 0


# %%
answers = ('possible' if solve(q) else 'impossible' for q in query)
print('\n'.join(answers))