#include <algorithm>
#include <atcoder/all>
#include <bitset>
#include <cassert>
#include <cmath>
#include <ctime>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
using namespace std;
using namespace atcoder;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n) - 1; i >= 0; i--)
#define repk(i, k, n) for (int i = k; i < (int)(n); i++)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
#define mod3 100000007
#define vi vector<int>
#define vs vector<string>
#define vc vector<char>
#define vl vector<ll>
#define vb vector<bool>
#define vvi vector<vector<int>>
#define vvc vector<vector<char>>
#define vvl vector<vector<ll>>
#define vvb vector<vector<bool>>
#define vvvi vector<vector<vector<int>>>
#define vvvl vector<vector<vector<ll>>>
#define pii pair<int, int>
#define pil pair<int, ll>
#define pli pair<ll, int>
#define pll pair<ll, ll>
#define vpii vector<pair<int, int>>
#define vpll vector<pair<ll, ll>>
#define vvpii vector<vector<pair<int, int>>>
#define vvpll vector<vector<pair<ll, ll>>>

template <typename T>
void debug(T e) {
    cerr << e << endl;
}

template <typename T>
void debug(vector<T> &v) {
    rep(i, v.size()) { cerr << v[i] << " "; }
    cerr << endl;
}

template <typename T>
void debug(vector<vector<T>> &v) {
    rep(i, v.size()) {
        rep(j, v[i].size()) { cerr << v[i][j] << " "; }
        cerr << endl;
    }
}

template <typename T>
void debug(vector<pair<T, T>> &v) {
    rep(i, v.size()) { cerr << v[i].first << " " << v[i].second << endl; }
}

template <typename T>
void debug(set<T> &st) {
    for (auto itr = st.begin(); itr != st.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(multiset<T> &ms) {
    for (auto itr = ms.begin(); itr != ms.end(); itr++) {
        cerr << *itr << " ";
    }
    cerr << endl;
}

template <typename T>
void debug(map<T, T> &mp) {
    for (auto itr = mp.begin(); itr != mp.end(); itr++) {
        cerr << itr->first << " " << itr->second << endl;
    }
}

void debug_out() { cerr << endl; }

template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << H << " ";
    debug_out(T...);
}

using mint = modint998244353;

void debug_mint1(vector<mint> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        cerr << vec[i].val() << " ";
    }
    cerr << endl;
}

void debug_mint2(vector<vector<mint>> &vec) {
    for (int i = 0; i < vec.size(); i++) {
        for (int j = 0; j < vec[i].size(); j++) {
            cerr << vec[i][j].val() << " ";
        }
        cerr << endl;
    }
}

int main() {
    ll N, L;
    cin >> N >> L;
    
    ll K;
    cin >> K;
    vector<ll> A(N);
    rep(i, N){
        cin >> A[i];
    }
    // 最大から二番目の値の最大化
    // つまり、「X 以上のものが 2 個以上あるように切る方法が存在するか？」という判定問題となる。
    // これは dp を使えばよさそう。
    vector<ll> B(N + 2);
    B[0] = 0;
    rep(i, N) B[i + 1] = A[i];
    B[N + 1] = L;

    ll ok = 0;
    ll ng = L + 1;
    while (ng - ok > 1){
        ll mid = (ok + ng) / 2;

        ll INF = N + 12;
        vector<vector<ll>> dp(K + 2, vector<ll>(3, INF));
        dp[0][0] = 0;
        for (ll i = 0; i <= K; i++){
            for (ll j = 0; j < 3; j++){
                if (dp[i][j] >= N + 1) continue;
                dp[i + 1][j] = min(dp[i + 1][j], dp[i][j] + 1);
                if (j <= 1){
                    auto it = lower_bound(all(B), B[dp[i][j]] + mid);
                    if (it == B.end()) continue;
                    ll nid = it - B.begin();
                    dp[i + 1][j + 1] = min(dp[i + 1][j + 1], nid);
                }
            }
        }
        // debug(mid);
        // debug(dp);
        if (dp[K + 1][2] < INF){
            ok = mid;
        }
        else{
            ng = mid;
        }
    }
    cout << ok << endl;
}