#include<bits/stdc++.h>
using namespace std;
typedef long double ld;
typedef long long ll;
#define rep(a, b) for(int a = 0; a < (b); ++a)
#define st first
#define nd second
#define pb push_back
#define all(a) a.begin(), a.end()
const ld EPS=1e-9;
const ll INF=1e9+7;
const int LIM=1e5+7;
ll T[LIM], n, k, t;
bool check(ll s) {
	ld p=t;
	for(int i=k; i<n-1; ++i) {
		p-=(ld)T[i]/(ld)(2*s);
		if(p<-EPS) return false;
		p+=t;
	}
	for(int i=k-1; i>=0; --i) {
		p-=(ld)T[i]/(ld)(2*s);
		if(p<-EPS) return false;
		p+=t;
	}
	return true;
}
ll solve(vector<ll>P) {
	rep(i, n-1) T[i]=P[i+1]-P[i];
	ll po=0, ko=INF;
	while(po<ko) {
		ll sr=(po+ko)/2;
		if(check(sr)) ko=sr; else po=sr+1;
	}
	return po;
}
int main() {
	ios_base::sync_with_stdio(0); cin.tie(0);
	cin >> n >> k >> t; --k;
	vector<ll>P(n);
	rep(i, n) cin >> P[i];
	ll ans=solve(P);
	rep(i, n) P[i]=P[n-1]-P[i];
	reverse(all(P));
	k=n-k-1;
	ans=min(ans, solve(P));
	cout << ans << '\n';
}