#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;
int n,k;
ll arr[100001];
ll val[100001];
bool check2(vl L, vl R)
{
int ptrL = 0;
int ptrR = 0;
ll maxL = L[0];
ll minR = R[0];
if(maxL < minR) return 0;
while(ptrL != siz(L)-1 || ptrR != siz(R)-1)
{
bool was = 0;
while(ptrL < siz(L)-1 && L[ptrL+1] >= minR)
{
was = 1;
maxL = max(maxL,L[++ptrL]);
}
while(ptrR < siz(R)-1 && R[ptrR+1] <= maxL)
{
was = 1;
minR = min(minR,R[++ptrR]);
}
if(!was) return 0;
}
return 1;
}
bool check(ll speed)
{
rep(i,n) val[i] = arr[i]-2*(ll)i*T*speed;
pll bestR = {1e18,-1};
pll bestL = {-1e18,-1};
rep2(i,0,k) bestL = max(bestL,{val[i],i});
rep2(i,k,n-1) bestR = min(bestR,{val[i],i});
vl L1,L2,R1,R2;
for(int i = k; i >= bestL.ss; i--) L1.pb(val[i]);
rep2(i,0,bestL.ss) L2.pb(val[i]);
rep2(i,k,bestR.ss) R1.pb(val[i]);
for(int i = n-1; i >= bestR.ss; i--) R2.pb(val[i]);
return check2(L1,R1) && check2(L2,R2);
}
int main()
{
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
//random_start();
cin >> n >> k >> T;
k--;
rep(i,n) cin >> 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";
}
