#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;unsigned short q[65536],rear,top,step[65536];//(2^16)-1bool vis[65536];unsigned short temp;bool bfs(){    memset(q,0,sizeof(q));    memset(vis,0,sizeof(vis));    rear=top=0;    q[top++]=temp;    step[temp]=0;    while(rear<top){        temp=q[rear++];        if(temp==0||temp==65535){            cout<<step[temp]<<endl;            return true;        }        short i=0;        for(;i<16;i++){            unsigned short ex=0;            ex|=1<<i;            if(i>3){                ex|=1<<(i-4);            }            if(i<12){                ex|=1<<(i+4);            }            if(i%4){                ex|=1<<(i-1);            }            if((i+1)%4){                ex|=1<<(i+1);            }            ex=ex^temp;            if(!vis[ex]){                vis[ex]=true;                q[top++]=ex;                step[ex]=step[temp]+1;            }        }    }    return false;}int main(){    //freopen("D:\\INPUT.txt","r", stdin);    short i=0;    temp=0;    for(;i<16;i++){        char c;        cin>>c;        //cout<<c<<endl;        if(c==‘b‘){            temp|=(1<<i);        }    }    if(!bfs()){        cout<<"Impossible\n";//"\b"打成"/n",WA    }    return 0;}