#include <vector>
#include <cmath>
#include <algorithm>
#include <numeric>
#include <climits>
using namespace std;
//#include "grader.cpp"
#include "boxes.h"

long long delivery(int N, int K, int L, int p[]){
    vector<long long>pre(K+1),suf(K+1);
    long long res=LLONG_MAX;
    for(int i=N-1;i>=0;i++)suf[i%K]+=L-p[i];
    for(int i=K-1;i<N;i++){
        int l=p[i-K+1],r=p[i];
        suf[i%K]-=L-p[i];
        if(i>=K)pre[i%K]+=p[i-K];
        int cost=min({L,2*r,2*(L-l)});
        res=min(res,cost+2*pre[i%K]+2*suf[(i+1)%K]);
    }
    if(N<=K)res=min(res,1LL*L);
    return res;
}