#include <bits/stdc++.h>
#include<cmath>
using namespace std;
int main() {
int q;
cin>>q;
while(q--) {
int n;
cin>>n;
const int N=2e5;
int a[N];
int freq[N]={0};
for(int i=0;i<n;i++) {
cin>>a[i];
freq[a[i]]++;
}
bool flag=false;
for(int i=0;i<n;i++) {
if(freq[a[i]]>=3) {
cout<<a[i]<<endl;
flag=true;
break;
}
}
if(flag==0) {
cout<<-1<<endl;
}
}
}
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