#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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