func_code_string: #include <bits/stdc++.h>   using namespace std;   void solve() {     long long n, o = 0, e = 0;     cin >> n;     vector<long long> a(n);     for (long long i = 0; i < n; ++i) {       cin >> a[i];     }     for (long long i = 0; i < n; ++i) {       if (a[i] % 2 != i % 2) {         if (a[i] % 2 == 0)           e++;         else           o++;       }     }     if (o == e) {       cout << o <<   n ;     } else {       cout << -1 <<   n ;     }   }   int32_t main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     long long t = 1;     cin >> t;     while (t--) {       solve();     }     return 0;   }   