#include <iostream>
#include <string>
using namespace std;

int main() {
	bool tmp2;
	int T, tmp1, tmp3, j;
	string S;
	cin >> T;
	for (int i = 0; i < T; ++i) {
		cin >> S;
		tmp1 = 0;
		tmp2 = false;
		tmp3 = 0;
		for (j = 0; j < S.size(); ++j) {
			if (S[j] == 'W') {
				++tmp1;
				tmp2 = true;
			}
			else if (S[j] == 'G') {
				if (tmp1 == 0) break;
				--tmp1;
				tmp2 = false;
				++tmp3;
			}
			else {
				if (tmp3 == 0) break;
				--tmp3;
			}
		}
		if (j != S.size() || tmp2 || tmp3) cout << "impossible";
		else cout << "possible";
		cout << endl;
	}
}