#include <bits/stdc++.h>
#include "boxes.h"
using namespace std;
#define pb push_back
#define ll long long
long long delivery(int N, int K, int L, int p[]) {
long long dp[N][2];
ll res=1e18;
for (int i = 0; i < N; ++i)
{
dp[i][0]=p[i]+min(p[i],L-p[i])+(i>=K ? dp[i-K][0] : 0);
}
for (int i = N-1; i >= 0; --i)
{
dp[i][1]= L-p[i] + min(p[i],L-p[i]) + (K+i<N ? dp[i+K][1] : 0);
res=min(res,(i ? dp[i-1][0] : 0) + dp[i][1]);
}
return res;
}
/*
static char _buffer[1024];
static int _currentChar = 0;
static int _charsNumber = 0;
static FILE *_inputFile, *_outputFile;
int main() {
#ifndef ONLINE_JUDGE
freopen("input.txt", "r", stdin);
freopen("output.txt", "w", stdout);
#endif
int N, K, L, i;
cin>>N>>K>>L;
int *p = (int*)malloc(sizeof(int) * (unsigned int)N);
for (i = 0; i < N; i++) {
cin>>p[i];
}
cout << delivery(N, K, L, p)<<endl;
return 0;
}*/
