#include <iostream>
#include <queue>
#include <climits>

using namespace std;

#define INFTY INT_MAX
#define NSTATE (1<<16)
#define FINALON ((1<<16)-1)
#define FINALOFF 0

int toStateInt( bool S[6][6] ) {
	int result = 0;
	for ( int i = 1; i <= 4; i++ )
		for ( int j = 1; j <= 4; j++ )
			if ( S[i][j] )
				result = (result << 1) | 1;
			else
				result = (result << 1) | 0;
	return result;
}

int makeNextState( bool S[6][6], int r, int c ) {
	const static int dr[] = {0, -1, +1, 0, 0};
	const static int dc[] = {0, 0, 0, -1, +1};

	for ( int i = 0; i < 5; i++ )
		S[r+dr[i]][c+dc[i]] = !S[r+dr[i]][c+dc[i]];

	int result = toStateInt(S);

	for ( int i = 0; i < 5; i++ )
		S[r+dr[i]][c+dc[i]] = !S[r+dr[i]][c+dc[i]];

	return result;
}

void toIntState( bool S[6][6], int sid ) {
	for ( int i = 4; i >= 1; i-- )
		for ( int j = 4; j >= 1; j-- )
			S[i][j] = ((sid & 1) == 1), sid >>= 1;
}

int compute( int init ) {
	queue<int> Q;
	bool visited[NSTATE];
	for ( int i = 0; i < NSTATE; i++ ) visited[i] = false;
	visited[init] = true;
	Q.push(init);

	for ( int d = 0; !Q.empty(); d++ )
		for ( int size = Q.size(); size > 0; size-- ) {
			const int state = Q.front(); Q.pop();

			if ( state == FINALON ) return d;
			if ( state == FINALOFF ) return d;

			bool S[6][6];
			toIntState(S, state);

			for ( int i = 1; i <= 4; i++ )
				for ( int j = 1; j <= 4; j++ ) {
					const int next = makeNextState(S, i, j);
					if ( visited[next] ) continue;
					visited[next] = true;
					Q.push(next);
				}
		}

	return INFTY;
}

int main() {
	char ch;

	while ( true ) {
		bool S[6][6];
		for ( int i = 1; i <= 4; i++ )
			for ( int j = 1; j <= 4; j++ ) {
				if ( !(cin >> ch) ) return 0;
				S[i][j] = (ch == 'b')? true : false;
			}

		const int initState = toStateInt(S);
		const int result = compute(initState);
		if ( result == INFTY )
			cout << "Impossible" << endl;
		else
			cout << result << endl;
	}

	return 0;
}