//UVa12545 - Bits Equalizer
//贪心
include
define MIN(X,Y) (((X)>(Y))?(Y):(X))
using namespace std;
int main(){

//freopen("UVa12545.in","r",stdin);

int N, kase = 0;

cin>>N;

while(N--){

string S,T;

int count = 0, bit[6];

bit[0] = bit[1] = bit[2] = bit[3] = bit[4] = 0;

cin>>S>>T;

for(int i = 0; i<S.size(); i++){

bit[T[i] -'0'+4]++;//all T[0];

if(S[i] != T[i])

if(S[i] == '?'){ count++; continue;}

else {bit[S[i]-'0']++; continue;}

bit[S[i]-'0'+2]++;//相等时候的s[0];

}

if(bit[2]+bit[0]+count < bit[4]){ cout<<"Case "<<++kase<<": -1\n"; continue;}

count += bit[0]+bit[1]-MIN(bit[0],bit[1]);

cout<<"Case "<<++kase<<": "<<count<<"\n";

}

return 0;

}

//已AC