#include <bits/stdc++.h>
using namespace std;
using ll=long long;
int main(){
	cin.tie(nullptr);
	ios::sync_with_stdio(false);
	int n;
	ll l;
	cin>>n>>l;
	int k;
	cin>>k;
	vector<ll> a(n+2);
	for(int i=0;i<n;i++)cin>>a[i+1];
	a[n+1]=l;
	ll ok=0,ng=l;
	k++;
	while(ok+1<ng){
		ll c=(ok+ng)/2;
		vector<vector<int>> dp(k+1,vector<int>(3,n+2));
		dp[0][0]=0;
		for(int i=0;i<k;i++){
			for(int j=0;j<3;j++){
				if(dp[i][j]==n+2)continue;
				dp[i+1][j]=min(dp[i+1][j],dp[i][j]+1);
				if(j<2){
					auto itr=ranges::lower_bound(a,a[dp[i][j]]+c);
					dp[i+1][j+1]=min(dp[i+1][j+1],(int)(itr-a.begin()));
				}
			}
		}
		if(dp[k][2]<=n+1)ok=c;
		else ng=c;
	}
	cout<<ok<<endl;

}