include

include

using namespace std;

/*Think of it this way: e.g.xaxb|bbxx left : 2x 1a 1b right: 2x 0a 2b , and they cancle out. What is left in the right is the answer.

O(n) per query*/

int arr[26];

int main() { ios::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);

int q;
cin >> q; 

string str; 
while(q--) {
    cin >> str; 
    if(str.size() % 2) { cout << -1 << '\n'; continue; }

    int mid = str.size() >> 1; 

    for(int i = 0; i < mid; ++i) ++arr[str[i] - 'a']; 

    int ret = 0; 
    for(int i = mid; i < str.size(); ++i) {
        if(arr[str[i] - 'a']) --arr[str[i] - 'a']; 
        else ++ret; 
    }

    cout << ret << '\n'; 
    memset(arr, 0, sizeof(arr)); 
}

return 0; 

}