#pragma GCC optimize("O3,unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#include <bits/stdc++.h>
#define int unsigned long long int
using namespace std;
typedef unsigned long long ll;
const int T = 350;
const int MOD = 1e9 + 7;
int32_t main(){
ios_base::sync_with_stdio(false);
cin.tie(nullptr);
priority_queue< pair<int , int> , vector<pair<int , int>> , greater<pair<int , int>>> pq;
vector<int> rng(1e6);
int n, t , k , ans = 0;
cin >> n >> t >> k;
vector<int> ds(k + 1);
for(int i = 1 ;i <= k ; i++)cin >> ds[i];
rng[0] = 1e9;
pq.push({ds[1] , 1});
while(true){
int value = pq.top().first , idx = pq.top().second , cmt = idx * 4;
pq.pop();
if(n <= cmt){
ans += n * value;
break;
}else{
ans += cmt * value;
n -= cmt;
}
if(rng[idx + 1] == rng[idx])pq.push({value + t , idx + 1});
rng[idx]++;
if(rng[idx] != rng[idx - 1] && rng[idx] < k )pq.push({ds[rng[idx] + 1] + t * (idx - 1) , idx});
}
cout << ans;
}
