func_code_string: #include <bits/stdc++.h>   using namespace std;   const int MAX_N = 1e5 + 1;   const long long MOD = 1e9 + 7;   const long long INF = 1e9;   void solve(long long a, long long b) {     if (a == 0 and b == 0) {       cout <<  0  << endl;     } else if (a == b) {       cout <<  1  << endl;     } else if (abs(a - b) % 2 == 1) {       cout <<  -1  << endl;     } else {       cout <<  2  << endl;     }     return;   }   int main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     cout.tie(0);     int tc = 1;     cin >> tc;     for (int t = 1; t <= tc; t++) {       long long a, b;       cin >> a >> b;       solve(a, b);     }   }   