func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long MOD = 1e9 + 7;   const long long inf = 1e18;   const long long N = 2e2 + 5;   long long n;   long long a[N];   void solve(long long id) {     cin >> n;     for (long long i = 0; i < n; i++) {       cin >> a[i];     }     long long odd = 0, even = 0;     long long oddind = 0, evenind = 0;     for (long long i = 0; i < n; i++) {       if (i % 2 != a[i] % 2) {         if (i % 2) {           oddind++;           even++;         } else {           evenind++;           odd++;         }       }     }     if (oddind == odd) {       cout << odd << endl;     } else       cout <<  -1  << endl;   }   int32_t main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     ;     long long t = 1;     cin >> t;     for (long long i = 1; i <= t; i++) solve(i);     return 0;   }   