F

#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define nl cout<<"\n";
#define sp cout<<" ";
#define sz(x) x.size()
#define NumOfDigit(w) log10(w) + 1
#define fill(arr, val)  memset(arr, val , sizeof(arr))
#define PI 3.141592654
#define ceil(w, m) (((w) / (m)) + ((w) % (m) ? 1 : 0))
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define fi first
#define se second
#define cin(v) for (auto&i:v) cin >> i;
#define cout(v) for (auto&i:v) cout << i << " ";
#define fixed(n) fixed << setprecision(n)
#define MOD  1000000007
using namespace std;

void zainab_hamdy(){
    ios_base::sync_with_stdio(false); cin.tie(nullptr); cout.tie(nullptr);
    //freopen("filename.in" , "r" ,stdin);
#ifndef ONLINE_JUDGE
    freopen("input.txt", "r", stdin), freopen("output.txt", "w", stdout);
#endif
}
/*#include <ext/pb_ds/assoc_container.hpp
#include <ext/pb_ds/tree_policy.hpp>

using namespace __gnu_pbds;

template <typename K, typename V, typename Comp = std::less<K>>
using ordered_map = tree<K, V, Comp, rb_tree_tag, tree_order_statistics_node_update>;
template <typename K, typename Comp = std::less<K>>
using ordered_set = ordered_map<K, null_type, Comp>;

template <typename K, typename V, typename Comp = std::greater_equal<K>>
using ordered_multimap = tree<K, V, Comp, rb_tree_tag, tree_order_statistics_node_update>;
template <typename K, typename Comp = std::greater_equal<K>>
using ordered_multiset = ordered_multimap<K, null_type, Comp>;

*/
bool prime(ll n){
    if(n==2 || n==3) return true;
    if(n<2 || n%2==0  ) return false;
    for(int i=3;i<=sqrt(n);i+=2)   if(n%i==0) return false;
    return true;
}


void isAccepted(){

int n ; cin >> n ;
ll odd=0, even=0 , x ;
for(int i=0; i<n ;i++){
    cin >> x ;
    if(x&1) odd++ ;
    else even ++;
}

if (even&1 and odd&1 )
cout << -1 ;

else if(even==0 or odd==0)
cout << 0;

else if( !even&1  and !odd&1)
cout << min(even/2 , odd/2);

else if (even&1==0)
cout<< even/2 ;

else
cout << odd/2 ;


nl

}
int main(){
      //        zainab_hamdy();

    int testCase=1;  // one test case
       cin >> testCase ;
 while(testCase--)
        isAccepted();  // my code

    return 0;
}