#include <bits/stdc++.h>
using namespace std;
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int64_t t;
  cin >> t;
  while (t--) {
    int64_t n;
    cin >> n;
    string s;
    cin >> s;
    int64_t br = 0;
    string ans = "";
    bool a = 0;
    for (int64_t i = 0; i < s.size(); i++) {
      int64_t x = s[i] - 48;
      if (x % 2 == 1) {
        ans += s[i];
        br++;
      }
      if (br == 2) {
        a = 1;
        break;
      }
    }
    if (a)
      cout << ans << "\n";
    else
      cout << "-1\n";
  }
}
