#include <iostream>
#include <sstream>
#include <iomanip>
#include <vector>
#include <string>
#include <map>
#include <set>
#include <algorithm>
#include <numeric>
#include <iterator>
#include <functional>
#include <complex>
#include <queue>
#include <stack>
#include <cmath>
#include <cassert>
#include <tuple>
using namespace std;
typedef long long LL;
typedef complex<double> CMP;

class BichromePainting { public:
	string isThatPossible(vector <string> board, int k)
	{
		return solve(board, k) ? "Possible" : "Impossible";
	}

	bool solve(vector<string> board, int K)
	{
		while(!no_black(board))
			if(!step_back(board, K))
				return false;
		return true;
	}

	bool no_black(const vector<string>& board)
	{
		const int H = board.size();
		const int W = board[0].size();
		for(int y=0; y<H; ++y)
		for(int x=0; x<W; ++x) if(board[y][x] == 'B')
			return false;
		return true;
	}

	bool step_back(vector<string>& board, int K) {
		bool updated = false;

		const int H = board.size();
		const int W = board[0].size();
		for(int y=0; y+K<=H; ++y)
		for(int x=0; x+K<=W; ++x) {
			bool has_white = false;
			bool has_black = false;
			for(int dy=0; dy<K; ++dy)
			for(int dx=0; dx<K; ++dx) {
				if(board[y+dy][x+dx]=='W') has_white=true;
				if(board[y+dy][x+dx]=='B') has_black=true;
			}
			if(has_white && has_black)
				continue;
			if(has_white || has_black) {
				for(int dy=0; dy<K; ++dy)
				for(int dx=0; dx<K; ++dx)
					board[y+dy][x+dx] = '*';
				updated = true;
			}
		}
		return updated;
	}
};

// BEGIN CUT HERE
#include <ctime>
double start_time; string timer()
 { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
 { os << "{ ";
   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
void verify_case(const string& Expected, const string& Received) {
 bool ok = (Expected == Received);
 if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
 cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
#define END	 verify_case(_, BichromePainting().isThatPossible(board, k));}
int main(){

CASE(0)
	string board_[] = {"BBBW",
 "BWWW",
 "BWWW",
 "WWWW"};
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 3; 
	string _ = "Possible"; 
END
CASE(1)
	string board_[] = {"BW",
 "WB"}
;
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 2; 
	string _ = "Impossible"; 
END
CASE(2)
	string board_[] = {"BWBWBB",
 "WBWBBB",
 "BWBWBB",
 "WBWBBB",
 "BBBBBB",
 "BBBBBB"}
;
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 2; 
	string _ = "Possible"; 
END
CASE(3)
	string board_[] = {"BWBWBB",
 "WBWBWB",
 "BWBWBB",
 "WBWBWB",
 "BWBWBB",
 "BBBBBB"}
;
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 2; 
	string _ = "Impossible"; 
END
CASE(4)
	string board_[] = {"BWBWBB",
 "WBWBWB",
 "BWBWBB",
 "WBWBWB",
 "BWBWBB",
 "BBBBBB"}
;
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 1; 
	string _ = "Possible"; 
END
CASE(5)
	string board_[] = {"BB",
 "BB"};
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 2; 
	string _ = "Possible"; 
END
CASE(6)
string board_[] = {"BBWW", "BBWW", "WBBW", "WWWW"};
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = 2; 
	string _ = "Possible"; 
END
/*
CASE(7)
	string board_[] = ;
	  vector <string> board(board_, board_+sizeof(board_)/sizeof(*board_)); 
	int k = ; 
	string _ = ; 
END
*/
}
// END CUT HERE
