#include<bits/stdc++.h>
typedef long long ll;
#define pb push_back
#define fr first
#define sc second
#define endl '\n'
using namespace std;
#define mid ((left+right)>>1)
const ll inf=2e18;
struct Seg{
int n;
vector<ll>mn,mx,arr;
void build(int node=1,int left=1,int right=-1){
if(right==-1)right=n;
if(left==right){
mn[node]=mx[node]=arr[left-1];
return;
}
build(node*2,left,mid);
build(node*2+1,mid+1,right);
mn[node]=min(mn[node*2],mn[node*2+1]);
mx[node]=max(mx[node*2],mx[node*2+1]);
}
void init(vector<ll>Arr){
arr=Arr;
n=arr.size();
mn.clear();
mx.clear();
mn.resize(n<<2,inf);
mx.resize(n<<2,-inf);
build();
}
int l,r;
ll x;
int sag(int node=1,int left=1,int right=-1){
if(right==-1)right=n;
if(left>r||right<l)return 0;
if(left>=l&&right<=r){
if(mx[node]<x)return 0;
if(left==right)return left;
if(mx[node*2+1]>=x)return sag(node*2+1,mid+1,right);
return sag(node*2,left,mid);
}
int x=sag(node*2+1,mid+1,right);
if(x==0)return sag(node*2,left,mid);
return x;
}
int en_sag(int left,int right,ll val){
l=left;r=right;x=val;
if(l>r)return 0;
return sag();
}
int sol(int node=1,int left=1,int right=-1){
if(right==-1)right=n;
if(left>r||right<l)return n+1;
if(left>=l&&right<=r){
if(mn[node]>=x)return n+1;
if(left==right)return left;
if(mn[node*2]<x)return sol(node*2,left,mid);
return sol(node*2+1,mid+1,right);
}
int x=sol(node*2,left,mid);
if(x==n+1)return sol(node*2+1,mid+1,right);
return x;
}
int en_sol(int left,int right,ll val){
l=left;r=right;x=val;
if(l>r)return n+1;
return sol();
}
};
int n,k;
ll t;
ll arr[100023];
Seg seg;
bool f(ll s){
ll o=s;
s*=2*t;
ll d=0;
vector<ll>v;
v.pb(0);
for(int i=k-1;i>=1;i--){
d+=s-(arr[i+1]-arr[i]);
v.pb(d);
}
reverse(v.begin(),v.end());
seg.init(v);
v.clear();
d=0;
v.pb(0);
for(int i=k+1;i<=n;i++){
d+=s-(arr[i]-arr[i-1]);
v.pb(d);
}
int p=1;
while(v.size()){
ll x=v.back();
v.pop_back();
p=seg.en_sag(1,seg.en_sol(p,k,-x)-1,-x)+1;
if(p==1)return false;
}
return p==k+1;
}
signed main(){
ios_base::sync_with_stdio(23^23);cin.tie(0);
cin>>n>>k>>t;
for(int i=1;i<=n;i++){
cin>>arr[i];
}
int l=0,r=1e9;
while(l<r){
ll s=(l+r)/2;
if(f(s))r=s;
else l=s+1;
}
cout<<l<<endl;
}
