#include <bits/stdc++.h>
using namespace std;
int32_t main(){
ios::sync_with_stdio(0);
cin.tie(0);
int n,k;
long long t;
cin >> n >> k >> t;
long long arr[n];
for(int i=0; i<n; i++) cin >> arr[i];
k--;
long long lo=0,hi=1e9+5,mid;
while(lo<hi){
mid=(lo+hi)/2;
vector<long long> lft,rgt;
for(int i=0; i<k; i++) lft.push_back(2ll*(arr[i+1]-arr[i]));
for(int i=n-1; i>k; i--) rgt.push_back(2ll*(arr[i]-arr[i-1]));
long long buff=t*mid;
while(!lft.empty()||!rgt.empty()){
if(rgt.empty()&&lft.back()<=2ll*buff){
buff-=lft.back()/2ll;
buff+=t*mid;
buff=min(buff,(long long)1e15);
lft.pop_back();
}
else if(lft.empty()&&rgt.back()<=2ll*buff){
buff-=rgt.back()/2ll;
buff+=t*mid;
buff=min(buff,(long long)1e15);
rgt.pop_back();
}
else if(lft.empty()||rgt.empty()) break;
else if(rgt.back()<lft.back()&&rgt.back()<=2ll*buff){
buff-=rgt.back()/2ll;
buff+=t*mid;
buff=min(buff,(long long)1e15);
rgt.pop_back();
}
else if(lft.back()<=rgt.back()&&lft.back()<=2ll*buff){
buff-=lft.back()/2ll;
buff+=t*mid;
buff=min(buff,(long long)1e15);
lft.pop_back();
}
else break;
}
if(lft.empty()&&rgt.empty()) hi=mid;
else lo=mid+1;
}
cout << (lo+1ll)/2ll;
}
