SECPASS Author

    #include<bits/stdc++.h>

    using namespace std;

    typedef long long ll;
    typedef pair<int, int> pii;

    #define F first
    #define S second

    const int MAXN = 1e5 + 10;

    int n, lst[200];;
    string s;

    int main(){
        ios::sync_with_stdio(false);
        cin.tie(0);
        int te; cin >> te;
        while (te--){
            memset(lst, -1, sizeof(lst));
            cin >> n >> s;

            vector<int> vec;
            for (int i = 0; i < n; i++)
                if (s[i] == s[0])
                    vec.push_back(i);

            int k = 1;
            while (k < n && s[k] != s[0]) k++;

            int ans = 1;
            while (ans+1 <= k){
                for (int pos: vec) {
                    if (pos + ans >= n) goto there;
                    if (s[pos+ans] != s[ans]) goto there;
                }
                ans++;
            }

    there:
            cout << s.substr(0, ans) << "\n";
        }
        return 0;
    }