#include <bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define ll long long
#define ld long double
#define ull unsigned long long
#define ff first
#define ss second
#define pii pair<int,int>
#define pll pair<long long, long long>
#define vi vector<int>
#define vl vector<long long>
#define pb push_back
#define rep(i, b) for(int i = 0; i < (b); ++i)
#define rep2(i,a,b) for(int i = a; i <= (b); ++i)
#define rep3(i,a,b,c) for(int i = a; i <= (b); i+=c)
#define count_bits(x) __builtin_popcountll((x))
#define all(x) (x).begin(),(x).end()
#define siz(x) (int)(x).size()
#define forall(it,x) for(auto& it:(x))
using namespace __gnu_pbds;
using namespace std;
typedef tree<int, null_type, less<int>, rb_tree_tag,tree_order_statistics_node_update> ordered_set;
//mt19937 mt;void random_start(){mt.seed(chrono::time_point_cast<chrono::milliseconds>(chrono::high_resolution_clock::now()).time_since_epoch().count());}
//ll los(ll a, ll b) {return a + (mt() % (b-a+1));}
const int INF = 1e9+50;
const ll INF_L = 1e18+40;
const ll MOD = 1e9+7;
ll T;
vl l_dif;
vl r_dif;
bool check(ll speed)
{
speed *= T;
int l_ptr = 0;
int r_ptr = 0;
ll cur_power = speed;
while(l_ptr < siz(l_dif) || r_ptr < siz(r_dif))
{
if(r_ptr == siz(r_dif) || (l_ptr != siz(l_dif) && l_dif[l_ptr] < r_dif[r_ptr]))
{
if(cur_power < l_dif[l_ptr]/2) return 0;
cur_power += -l_dif[l_ptr]/2+speed;
l_ptr++;
}
else
{
if(cur_power < r_dif[r_ptr]/2) return 0;
cur_power += -r_dif[r_ptr]/2+speed;
r_ptr++;
}
}
return 1;
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
int n,k;
cin >> n >> k >> T;
vl arr(n);
rep(i,n) cin >> arr[i];
rep(i,n) arr[i] *= 2;
T *= 2;
rep(i,k-1) l_dif.pb(arr[i+1]-arr[i]);
reverse(all(l_dif));
rep2(i,k-1,n-2) r_dif.pb(arr[i+1]-arr[i]);
ll l = 0;
ll r = 3e9;
ll ans = -1;
while(l <= r)
{
ll mid = (l+r)/2;
if(check(mid))
{
ans = mid;
r = mid-1;
}
else
{
l = mid+1;
}
}
cout << ans << "\n";
}
