#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  ll t, n, i, j, k;
  cin >> t;
  while (t--) {
    string s;
    cin >> n;
    cin >> s;
    j = 0;
    string t = "";
    for (i = 0; i < s.size(); i++) {
      if ((s[i] - '0') % 2 != 0) j++;
      t += s[i];
      if (j == 2) break;
    }
    if (j >= 2)
      cout << t << endl;
    else
      cout << "-1" << endl;
  }
  return 0;
}
