#include <cstdio>#include <cstring>#include <queue>#include <iostream>using namespace std;int step;int bfs(int start){	queue<int> Queue;	int book[65536],last=start;	memset(book,0,sizeof(book));	Queue.push(start);	book[start]=1;	step=0;	while(!Queue.empty()){		int head=Queue.front();		Queue.pop();		if(head==0||head==65535){			return 1;		}		for(int i=0;i<16;i++){			int temp=head^(1<<i);			if((i+1)%4)				temp=temp^(1<<(i+1));			if(i%4)				temp=temp^(1<<(i-1));			if(i>3)				temp=temp^(1<<(i-4));			if(i<12)				temp=temp^(1<<(i+4));			if(!book[temp]){				book[temp]=1;				Queue.push(temp);			}		}		if(head==last){			step++;			last=Queue.back();		}	}	return 0;}int main(){	char ch;	int t,start=0;	for(int i=0;i<16;i++){		ch=getchar();		t=(ch=='b'?1:0);		start=(t<<i)+start;		if((i+1)%4==0){			getchar();		}	}	int flag=bfs(start);	if(flag){		cout<<step<<endl;	}	else{		cout<<"Impossible/n";	}	return 0;}