#include <bits/stdc++.h>
using namespace std;
#define SC               scanf
#define PF               printf
#define ull              unsigned long long
#define ld               long double
#define D                double
#define F                first
#define S                second
#define pb               push_back
#define pf               push_front
#define MP               make_pair
#define sort_a(a)        sort(a.begin(),a.end());
#define sort_d(a)        sort(a.rbegin(),a.rend());
#define READ(f)          freopen(f, "r", stdin)
#define WRITE(f)         freopen(f, "w", stdout)
#define rev(s)           reverse(s.begin(),s.end())
#define it(it,mp)        for(auto it=mp.begin() ; it!=mp.end() ; it++)
#define IOS              ios_base :: sync_with_stdio(false); cin.tie(NULL);
const int N = 1e5 + 5;
const int inf = 1e9 + 1;
const double eps = 1e-15;
const double EPS = 1e-9;
const double PI = acos(-1.0);
typedef long long int                   ll;
typedef pair<int,int>                   PII;
int main()
{
    IOS
    // READ("test.txt");
    //WRITE("");
    ll t, n ;
    string s;
    cin >> t ;
    while(t--)
    {
        cin >> n>> s;
        bool flag = true;
        int cnt =0 ,pos =0 , pp = 0,ok=0;
        for(int i=0 ; i<n ; i++)
        {
            int tt = s[i]-'0';
            if(tt&1 ){
                cnt++;
                if(ok==0){
                    pos = i,ok=1;
                }
            }

                if(cnt >1 && tt&1)pp = i ;

        }
        if(cnt<=1)
        {
            cout<<-1<<endl;
        }
        else
        {
            if(cnt&1)
            {
                for(int i=0 ; i<n ; i++)
                {
                    if(i ==pp ){
                        cout<<s[s.size()-1];
                        }
                        else if(i==n-1){
                            cout<<s[pp];
                        }
                    else if(i!=pos)
                        cout<<s[i];

                }
                cout<<endl;
            }
            else
            {
               // cout<<pos<<pp<<endl;
                for(int i=0 ; i<n ; i++)
                {
                    if(i ==pp ){
                        cout<<s[s.size()-1];
                        }
                       else if(i==n-1){
                            cout<<s[pp];
                        }
                   else cout<<s[i];
                }
                cout<<endl;
            }

        }
    }
    return 0;
}