#include<bits/stdc++.h>
#include<fstream>
using namespace std;
ifstream fin("FEEDING.INP");
ofstream fout("FEEDING.OUT");
#define sz(a) (int)a.size()
#define ll long long
#define pb push_back
#define forr(i, a, b) for(int i = a; i < b; i++)
#define dorr(i, a, b) for(int i = a; i >= b; i--)
#define ld long double
#define vt vector
#include<fstream>
#define fi first
#define se second
#define pll pair<ll, ll>
#define pii pair<int, int>
const ld PI = 3.14159265359;
using u128 = __uint128_t;
const int x[4] = {1, -1, 0, 0};
const int y[4] = {0, 0, 1, -1};
const ll mod = 1e9 + 7, inf = 1e9;
const int mxn = 3e5 + 5;
int n, p, q;
int dis[2005][2005], a[2005];
bool ck(int mid){
forr(i, 1, n + 2){
forr(j, 0, p + 1){
dis[i][j] = inf;
}
}
deque<pii>dq;
dq.pb({1, 0}); dis[1][0] = 0;
while(!dq.empty()){
auto [id, small] = dq.front(); dq.pop_front();
if(id == n + 1){
return(dis[id][small] <= q);
}
int nwid = upper_bound(a + 1, a + n + 1, a[id] + mid - 1) - a;
if(small < p && dis[nwid][small + 1] > dis[id][small]){
dis[nwid][small + 1] = dis[id][small];
dq.push_front(make_pair(nwid, small + 1));
}nwid = upper_bound(a + 1, a + n + 1, a[id] + 2 * mid - 1) - a;
if(dis[nwid][small] > dis[id][small] + 1){
dis[nwid][small] = dis[id][small] + 1;
dq.pb(make_pair(nwid, small));
}
}
return(0);
}
signed main()
{
ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
cin >> n >> p >> q; p = min(p, n);
for(int i = 1; i <= n; i++){
cin >> a[i];
}
sort(a + 1, a + n + 1);
int l = 0, r = 5e8, ans = -1;
while(l <= r){
int mid = (l + r) >> 1;
if(ck(mid)){
ans = mid; r = mid - 1;
}else{
l = mid + 1;
}
}
cout << ans;
return(0);
}
