#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;


int main() {
    int testCases;
    cin >> testCases;

    for(int i = 0; i < testCases; i++) {
        string tab;
        cin >> tab;
        int tabSize = tab.size();
        if(tab.size() % 2 != 0) {
            cout << -1 << endl;
            continue;
        }
        int counter = 0;
        for(int j = 0; j < tabSize / 2; j++) {
            for(int k = tabSize / 2 + counter; k < tabSize; k++) {
                if(tab[j] == tab[k]) {
                    swap(tab[tabSize / 2 + counter], tab[k]);
                    counter++;
                    break;
                }
            }
        }
        cout << tabSize / 2 - counter << endl;
    }
    return 0;
}