#include <iostream>
#include <vector>
using std::cin;
using std::cout;
using std::endl;
using std::vector;
int checkFreq(const vector<int>& a) {
vector<int> freq(10001, 0);
for (int num : a) {
freq[num]++;
if (freq[num] >= 3) {
return num;
}
}
return -1;
}
int main() {
int t;
cin >> t;
for (int i = 0; i < t; i++) {
int n;
cin >> n;
vector<int> a(n);
for (int j = 0; j < n; j++) {
cin >> a[j];
}
cout << checkFreq(a) << endl;
}
return 0;
}
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