#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using vll = vector<ll>;
using vi = vector<int>;
using vvll = vector<vll>;
using vvi = vector<vi>;
#define sz(x) int(x.size())
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
ll N, K, T;
cin >> N >> K >> T;
vll X(1+N);
for(int i = 1; i <= N; i++)
{
cin >> X[i];
}
ll lo = 0, hi = ((((1'000'000'000'000'000'000LL / 2LL + 1) / N) + 1) / T) + 1;
// ll lo = 1, hi = 1'000'000'000'000'000'000LL/N;
// ll lo = 0, hi = 5;
//
while(lo != hi)
{
// cerr << "\n\n\n\n\n searching " << lo << ' ' << hi << '\n';
ll mid = (lo + hi)/2;
// cerr << "mid = " << mid << "\n";
vll Y(1+N);
for(ll i = 1; i <= N; i++)
{
Y[i] = 2LL * T * mid * i - X[i];
}
if(Y[1] > Y[N])
{
lo = mid + 1;
continue;
}
int il = K, ir = K;
// for(int i = 1; i <= N; i++)
// cerr << Y[i] << ' ';
// cerr << '\n';
for(int t = 0; 1; t++)
{
if(t % 2 == 0)
{
int ln = il;
for(int i = il-1; i >= 1; i--)
{
if(Y[i] <= Y[ln])
ln = i;
if(Y[i] > Y[ir])
break;
}
if(ln == il && t >= 2)
break;
else
il = ln;
}
else
{
int rn = ir;
for(int i = ir+1; i <= N; i++)
{
if(Y[i] >= Y[rn])
rn = i;
if(Y[i] < Y[il])
break;
}
if(rn == ir && t >= 2)
break;
else
ir = rn;
}
}
int ul = 1, ur = N;
for(int t = 0; 1; t++)
{
if(t % 2 == 0)
{
int ln = ul;
for(int i = ul+1; i <= K; i++)
{
if(Y[i] <= Y[ln])
ln = i;
if(Y[i] > Y[ur])
break;
}
if(ln == ul && t >= 2)
break;
else
ul = ln;
}
else
{
int rn = ur;
for(int i = ur-1; i >= K; i--)
{
if(Y[i] >= Y[rn])
rn = i;
if(Y[i] < Y[ul])
break;
}
if(rn == ur && t >= 2)
break;
else
ur = rn;
}
}
if(il <= ul && ur <= ir)
hi = mid;
else
lo = mid+1;
}
cout << hi << '\n';
}
