#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, l;
  cin >> n >> l;
  int k;
  cin >> k;
  VI a(n + 2);
  rep(i, n) cin >> a[i + 1];
  a[n + 1] = l;
  n += 2;
  int bad = l, ok = 0;
  while (bad - ok > 1) {
    int c = (bad + ok) / 2;
    constexpr int INF = 1001001001;
    VI dp1(n, INF), dp2(n, INF);
    int j = 0;
    rep(i, n) {
      while (j < n && a[j] - a[i] < c) j++;
      if (j < n) {
        chmin(dp2[j], dp1[i] + j - i - 1);
        chmin(dp1[j], j - i - 1);
      }
      if (i + 1 < n) chmin(dp1[i+1], dp1[i]), chmin(dp2[i+1], dp2[i]);
    }
    (n - 1 - *min_element(all(dp2)) >= k + 1 ? ok : bad) = c;
  }
  cout << ok << '\n';
}