#include "boxes.h"
#include <bits/stdc++.h>
// #include <ext/rope>
// #include <ext/pb_ds/assoc_container.hpp>
// using namespace __gnu_pbds;
// using namespace __gnu_cxx;
using namespace std;
// #define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
#define ll long long
#define ull unsigned long long
#define ld long double
#define pb push_back
#define bit(mask, i) ((mask >> i) & 1)
#define el '\n'
#define F first
#define S second
template <class X, class Y> bool maximize(X &x, const Y &y) { return (x < y ? x = y, 1 : 0); }
template <class X, class Y> bool minimize(X &x, const Y &y) { return (x > y ? x = y, 1 : 0); }
const int INF = 1e9;
const ll LINF = 1e18;
const int MOD = 1e9 + 7;
const int MULTI = 0;
const ld eps = 1e-9;
const int dx[4] = {0, 1, 0, -1}, dy[4] = {1, 0, -1, 0}; // R D L U
const int ddx[4] = {-1, 1, 1, -1}, ddy[4] = {1, 1, -1, -1}; // UR DR DL UL
const char cx[4] = {'R', 'D', 'L', 'U'};
const ll base = 31;
const int nMOD = 2;
const ll mods[] = {(ll)1e9 + 10777, (ll)1e9 + 19777, (ll)1e9 + 3, (ll)1e9 + 3777};
const int maxn = 1e7 + 5;
int n, k, l, pos[maxn];
ll res;
int dist(int u, int v) {
if (u > v) swap(u, v);
return min(v - u, u + l - v);
}
int calc(int le, int ri) {
return min(pos[ri] + dist(0, pos[ri]), l - pos[le] + dist(0, pos[le]));
}
void solve() {
int ptl = 0, ptr = n - 1;
while (1)
if (ptl + k - 1 < ptr - k + 1) {
if (calc(ptl, ptl + k - 1) < calc(ptr - k + 1, ptr))
res += calc(ptl, ptl + k - 1), ptl += k;
else
res += calc(ptr - k + 1, ptr), ptr -= k;
} else {
if (calc(ptl, ptl + k - 1) < calc(ptr - k + 1, ptr))
res += calc(ptl, ptl + k - 1), ptl += k;
else
res += calc(ptr - k + 1, ptr), ptr -= k;
if (ptl <= ptr) res += calc(ptl, ptr);
break;
}
}
ll delivery(int N, int K, int L, int p[]) {
n = N; k = K; l = L;
for (int i = 0; i < n; ++i)
pos[i] = p[i];
solve();
return res;
}
