/* Author : Mychecksdead */
#include<bits/stdc++.h>
using namespace std;
#define ll long long int
#define MOD (1000000000+7)
#define MOD1 (998244353)
#define pb push_back
#define all(x) x.begin(), x.end()
#define en cout << '\n'
#define ff first
#define ss second
#define pii pair<int,int>
#define vi vector<int>
const int N = 1e6+100, M = 1e5+10, K = 52, MX = 30;
int n, k;
ll t, a[N];
void solve(){
cin >> n >> k >> t;
for(int i = 1; i <= n; ++i){
cin >> a[i];
}
ll l = 0, r = 1e9, ans = 1e9;
while(l <= r){
ll mid = l+r>>1;
bool ok = false;
for(int mask = 0; mask < (1<<(n-1)); ++mask){
if(__builtin_popcount(mask) != k - 1) continue;
// 1's go left, 0's go right
ll mn = a[k], mx = a[k];
bool oo = true;
int L = k, R = k;
if(mid == 7)
for(int i = 0; i < n-1; ++i){
if((1<<i)&mask){
// if(mid==7){
// cerr << i << ' ' << a[L] + (a[R] - a[L + 1]) << '\n';
// }
--L; // we will get a[L-1]
if(mn > a[L] + (a[R] - mn) + t * mid * 2){
oo = false;
break;
}
mx = a[L] + (a[R] - mn) + t * mid;
mn = mn - t * mid;
}else{
++R; // we will get a[L-1]
if(mx < a[R] - (mx - a[L]) - t * mid * 2){
oo = false;
break;
}
mn = a[R] - (mx - a[L]) - t * mid;
mx = mx + t * mid;
}
}
if(oo){
ok = 1;
break;
}
}
if(ok){
ans = mid;
r = mid-1;
}else l = mid+1;
}
cout << ans;
}
int main(){
cin.tie(0); ios::sync_with_stdio(0);
int tt = 1, aa;
// freopen("in.txt", "r", stdin);
// freopen("out.txt", "w", stdout);
while(tt--){
solve();
en;
}
cerr<<"time taken : "<<(float)clock()/CLOCKS_PER_SEC<<" seconds\n";
return 0;
}
