#include <iostream>
using namespace std;
int a[10005];
int b[10005];
int main()
{
    int t;
    cin >> t;
    while (t--)
    {
        int n;
        cin >> n;
        int sum = 0;
        for (int i = 1; i <= n; i++) {
            cin >> a[i];
            if (a[i] == 1) sum++;
        }
        for (int i = 1; i <= n; i++) {
            cin >> b[i];
            if (b[i] == 1) sum++;
        }
        if (sum % 2 == 1) {
            cout << -1 << endl;
            continue;
        }
        int sum1 = 0, sum2 = 0;
        for (int i = 1; i <= n; i++) {
            if (a[i] != b[i]) {
                if (a[i] == 1) sum1++;
                else sum2++;
            }
        }
        if (sum1 % 2 == 0) cout << (sum1 + sum2) / 2 << endl;
        else cout << sum1 / 2 + sum2 / 2 + 2 << endl;
    }
    return 0;
}