#include<iostream>
using namespace std;
 
 
int checkFreq(int a[], int n){
    int freq[1001] = {0};
    for (int i=0; i<n; i++){
        freq[a[i]]++;
    }
    for (int i=0; i<1001; i++){
        if (freq[i] == 3){
            cout << i;
            return i;
            break;
        }
    }
    return -1;
 
}
 
 
int main() {
    int t;
    cin >> t;
 
    for (int i=0; i<t; i++){
        int n;
        cin >> n;
        int a[n];
        for (int j=0; j<n; j++){
            cin >> a[j];
        }
        cout << checkFreq(a, n) << endl;
 
    }
 
}

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7
1
1
3
2 2 2
7
2 2 3 3 4 2 2
8
1 4 3 4 3 2 4 1
9
1 1 1 2 2 2 3 3 3
5
1 5 2 4 3
4
4 4 4 4