#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 4000000000000000001LL

int main(){
	
	int N,L;
	cin>>N>>L;
	int K;
	cin>>K;
	vector<long long> a(N);
	rep(i,N){
		cin>>a[i];
	}
	a.push_back(L);
	a.insert(a.begin(),0);
	N = a.size();
	long long ok = 0,ng = L+1;
	while(ng-ok>1LL){
		long long mid = (ok+ng)/2;
		vector dp(N,vector<int>(3,-Inf32));
		dp[0][0] = 0;
		rep(i,N-1){
			rep(j,3){
				dp[i+1][j] = max(dp[i][j]+1,dp[i+1][j]);
				int d = distance(a.begin(),lower_bound(a.begin(),a.end(),a[i] + mid));
				if(j!=2 && d != a.size()){
					dp[d][j+1] = max(dp[i][j]+1,dp[d][j+1]);
				}
			}
		}
		if(dp[N-1][2] >= K+1)ok = mid;
		else ng = mid;
	}
	cout<<ok<<endl;
	return 0;
}