#include<bits/stdc++.h>
using namespace std;

int main(){
  using ll=long long;
  ll inf=1e18;
  ll n,l,k;
  cin>>n>>l>>k;
  vector<ll> a(n+1);
  a[0]=0;
  for (int i=1;i<=n;i++) cin>>a[i];
  a.push_back(l);
  a.push_back(inf);
  auto f=[&](ll x){
    vector<ll> g(n+3,inf);
    ll mval=inf;
    int r=0;
    ll len=0;
    ll mcnt=-inf;
    for (int i=0;i<=n;i++){
      while (a[r]-a[i]<x) r++;
      if (r==n+2) break;
      g[r]=min(g[r],(ll)r-i);
      mval=min(mval,g[i]);
      mcnt=max(mcnt,n+1-(mval+r-i));
    }
    return mcnt>=k-1;
  };
  ll L=0,R=2e9;
  while (R-L>1){
    ll mid=(L+R)/2;
    if (f(mid)) L=mid;
    else R=mid;
  }
  cout<<L<<endl;
}