#include <iostream>
#include <string>
#include <cstring>
#include <stack>

using namespace std;

bool judge(string);

int main(int argc, char *argv[]) {
	int T;
	string pattern;
	cin >> T;
	for (int i = 0; i < T; i++) {
		cin >> pattern;
		cout << (judge(pattern) ? "possible" : "impossible") << endl;
	}
}
bool judge(string s) {
	int numOfWhite = 0;
	int numOfGreen = 0;
	int lastW;
	int lastG;
	int len = s.length();
	char *c = (char *)malloc(sizeof(char) * len + 1);
	strcpy(c, s.c_str());
	for (int i = 0; i < len; i++) {
		if (c[i] == 'W') {
			numOfWhite++;
			lastW = i;
		} else if (c[i] == 'G') {
			if (numOfWhite < 1) {
				return false;
			}
			numOfGreen++;
			lastG = i;
		} else {
			if (numOfGreen > 0) {
				numOfWhite--;
				numOfGreen--;
			} else {
				return false;
			}
		}
	}
	if (numOfGreen > 0) {
		return false;
	}
	if (lastW > lastG) {
		return false;
	}
	return true;
}