//#pragma GCC target("avx2")
//#pragma GCC optimize("O3")
//#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int,int>;
using pll = pair<ll,ll>;
using pli = pair<ll,int>;
#define AMARI 998244353
//#define AMARI 1000000007
#define el '\n'
#define El '\n'
#define YESNO(x) ((x) ? "Yes" : "No")
#define YES YESNO(true)
#define NO YESNO(false)
#define REV_PRIORITY_QUEUE(tp) priority_queue<tp,vector<tp>,greater<tp>>
#define EXIT_ANS(x) {cout << (x) << '\n'; return;}
template <typename T> void inline SORT(vector<T> &v){sort(v.begin(),v.end()); return;}
template <typename T> void inline VEC_UNIQ(vector<T> &v){sort(v.begin(),v.end()); v.erase(unique(v.begin(),v.end()),v.end()); return;}
template <typename T> T inline MAX(vector<T> &v){return *max_element(v.begin(),v.end());}
template <typename T> T inline MIN(vector<T> &v){return *min_element(v.begin(),v.end());}
template <typename T> T inline SUM(vector<T> &v){T ans = 0; for(int i = 0; i < (int)v.size(); i++)ans += v[i]; return ans;}
template <typename T> void inline DEC(vector<T> &v){for(int i = 0; i < (int)v.size(); i++)v[i]--; return;}
template <typename T> void inline INC(vector<T> &v){for(int i = 0; i < (int)v.size(); i++)v[i]++; return;}
void inline TEST(void){cerr << "TEST" << endl; return;}
template <typename T> bool inline chmin(T &x,T y){
    if(x > y){
        x = y;
        return true;
    }
    return false;
}
template <typename T> bool inline chmax(T &x,T y){
    if(x < y){
        x = y;
        return true;
    }
    return false;
}
template <typename T = long long> vector<T> inline get_vec(int n){
    vector<T> ans(n);
    for(int i = 0; i < n; i++)cin >> ans[i];
    return ans;
}
template <typename T> void inline print_vec(vector<T> &vec,bool kaigyou = false){
    int n = (int)vec.size();
    for(int i = 0; i < n; i++){
        cout << vec[i];
        if(kaigyou || i == n - 1)cout << '\n';
        else cout << ' ';
    }
    if(!n)cout << '\n';
    return;
}
template <typename T> void inline debug_vec(vector<T> &vec,bool kaigyou = false){
    int n = (int)vec.size();
    for(int i = 0; i < n; i++){
        cerr << vec[i];
        if(kaigyou || i == n - 1)cerr << '\n';
        else cerr << ' ';
    }
    if(!n)cerr << '\n';
    return;
}
vector<vector<int>> inline get_graph(int n,int m = -1,bool direct = false){
    if(m == -1)m = n - 1;
    vector<vector<int>> g(n);
    while(m--){
        int u,v;
        cin >> u >> v;
        u--; v--;
        g[u].push_back(v);
        if(!direct)g[v].push_back(u);
    }
    return g;
}

vector<int> make_inv(vector<int> p){
    int n = (int)p.size();
    vector<int> ans(n);
    for(int i = 0; i < n; i++)ans[p[i]] = i;
    return ans;
}

bool func(vector<ll> x,int k,ll l,ll val){
    //任意の点について、 ±val の範囲に x が k 個以上ある必要がある
    //x[i] + val + 1 ,x[i] - val - 1 を良い感じに調べれば良さそう
    if(val > l / 2)return true;
    int n = (int)x.size();
    for(int i = 0; i < n; i++){
        x.push_back(x[i] + l);
    }
    for(int i = 0; i < n; i++){
        x.push_back(x[i] + 2LL * l);
    }

    for(int i = 0; i < n; i++){
        //x[i] + val + 1
        ll tempx = x[i] + val;
        vector<ll>::iterator itl = upper_bound(x.begin(),x.end(),tempx - val);
        vector<ll>::iterator itr = upper_bound(x.begin(),x.end(),tempx + val);
        if(distance(itl,itr) < k)return false;
    }
    for(int i = 2 * n; i < 3 * n; i++){
        //x[i] - k - 1
        ll tempx = x[i] - val;
        vector<ll>::iterator itl = lower_bound(x.begin(),x.end(),tempx - val);
        vector<ll>::iterator itr = lower_bound(x.begin(),x.end(),tempx + val);
        if(distance(itl,itr) < k)return false;
    }
    return true;


}

#define MULTI_TEST_CASE true 
void solve(void){
    //問題を見たらまず「この問題設定から言えること」をいっぱい言う
    //よりシンプルな問題に言い換えられたら、言い換えた先の問題を自然言語ではっきりと書く
    //複数の解法のアイデアを思いついた時は全部メモしておく
    //g++ -D_GLIBCXX_DEBUG -Wall -O2 d.cpp -o o
    int n;
    cin >> n;
    ll l; int k;
    cin >> l >> k;
    vector<ll> x = get_vec(n);
    SORT(x);
    
    ll ok = 2 * l,ng = 0;
    while(ok - ng >= 2){
        ll mid = (ok + ng) / 2;
        if(func(x,k,l,mid))ok = mid;
        else ng = mid;
    }
    cout << ok << el;
    return;
}

void calc(void){
    return;
}

signed main(void){
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    calc();
    int t = 1;
    if(MULTI_TEST_CASE)cin >> t;
    while(t--){
        solve();
    }
    return 0;
}