#include <bits/stdc++.h>
using namespace std;
template <typename T>
T gcd(T a, T b) {
  if (a == 0) return b;
  return gcd(b % a, a);
}
template <typename P>
P dectobin(P a) {
  if (a == 0)
    return 0;
  else
    return (a % 2 + 10 * dectobin(a / 2));
}
template <typename Y>
Y bintodec(Y a) {
  long long ans = 0, b = 1, t = a;
  while (t) {
    long long ld = t % 10;
    t /= 10;
    ans += ld * b;
    b = b * 2;
  }
  return ans;
}
template <typename H>
H modExp(H x, H n) {
  long long r = 1;
  while (n > 0) {
    if (n % 2 == 1) {
      r = (r * x) % 1000000007;
    }
    x = (x * x) % 1000000007;
    n /= 2;
  }
  return r;
}
template <typename T>
T isPowerOfTwo(T x) {
  return x && (!(x & (x - 1)));
}
template <typename T>
T lcm(T a, T b) {
  return a * b / gcd(a, b);
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ostream_iterator<long long> output(cout, " ");
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    string second;
    cin >> second;
    vector<long long> v;
    for (long long(i) = (0); i < (n); i++) {
      long long k = (long long)(second[i] - '0');
      if (k % 2 != 0) {
        v.emplace_back(k);
      }
    }
    if (v.size() < 2)
      cout << -1 << '\n';
    else
      cout << v[0] << v[1] << '\n';
  }
  return 0;
}
