#include <bits/stdc++.h> using namespace std; const int N = 1e7 + 7; long long delivery(int n, int k, int l, int *positions){ sort(positions, positions + n); vector<long long> v1, v2; int idx = 0; for(; idx < n && positions[idx] <= l / 2; idx++){ v1.push_back(positions[idx]); } for(; idx < n; idx++){ v2.push_back(l - positions[idx]); } reverse(v2.begin(), v2.end()); long long ans = 0; vector<long long> v3, v4; for(int i = k - 1; true; i += k){ ans += (long long)v1[i] * 2ll; if(i + k >= (int)v1.size()){ for(++i; i < (int)v1.size(); i++){ v3.push_back(v1[i]); } break; } } for(int i = k - 1; true; i += k){ ans += (long long)v2[i] * 2ll; if(i + k >= (int)v2.size()){ for(++i; i < (int)v2.size(); i++){ v4.push_back(v2[i]); } break; } } if(v3.empty() || v4.empty()){ if(!v3.empty()){ ans += v3.back() * 2ll; } if(!v4.empty()){ ans += v4.back() * 2ll; } return ans; } return ans; }