#include<bits/stdc++.h>
#define forin(i, a, b) for(int i = a; i <= b; i++)
#define forde(i, a, b) for(int i = a; i >= b; i--)
#define fi first
#define se second
#define ll long long
using namespace std;
const int N = 1e7 + 10;
ll dp[2][N];
ll delivery(int n, int k, int l,int a[])
{
ll res = 1e18;
//forin(i, 1, n) cin >> a[i];
forin(i, 1, n) dp[0][i] = dp[0][max(0, i-k)] + a[i-1] + min(a[i-1], l-a[i-1]);
forde(i, n, 1) dp[1][i] = dp[1][min(n+1, i+k)] + l-a[i-1] + min(a[i-1], l - a[i-1]);
forin(i, 1, n+1) res = min(res, dp[0][i-1] + dp[1][i]);
//forde(i, n, 1) cout << dp[1][i]<<" ";
return res;
}
