#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define MASK(i) (1LL << (i))
#define GETBIT(mask, i) (((mask) >> (i)) & 1)
#define ALL(v) (v).begin(), (v).end()
ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll gcd(ll a, ll b){return __gcd(a, b);}
ll lcm(ll a, ll b){return a / gcd(a, b) * b;}
ll LASTBIT(ll mask){return (mask) & (-mask);}
int pop_cnt(ull mask){return __builtin_popcountll(mask);}
int ctz(ull mask){return __builtin_ctzll(mask);}
int logOf(ull mask){return 63 - __builtin_clzll(mask);}
mt19937_64 rng(chrono::high_resolution_clock::now().time_since_epoch().count());
ll rngesus(ll l, ll r){return l + (ull) rng() % (r - l + 1);}
double rngesus_d(double l, double r){
double wow = (double) ((ull) rng()) / ((ull)(0-1));
return wow * (r - l) + l;
}
template <class T1, class T2>
bool maximize(T1 &a, T2 b){
if (a < b) {a = b; return true;}
return false;
}
template <class T1, class T2>
bool minimize(T1 &a, T2 b){
if (a > b) {a = b; return true;}
return false;
}
template <class T>
void printArr(T container, string separator = " ", string finish = "\n", ostream &out = cout){
for(auto item: container) out << item << separator;
out << finish;
}
template <class T>
void remove_dup(vector<T> &a){
sort(ALL(a));
a.resize(unique(ALL(a)) - a.begin());
}
struct Node{
ll cost, h, d;
Node(ll cost, ll h, ll d): cost(cost), h(h), d(d){}
};
struct compare{
bool operator () (Node a, Node b){return a.cost > b.cost;}
};
ll get_amount(ll x){
return (x+1) * (x+1) - (x-1) * (x-1);
}
void solve(){
ll n, t, k; cin >> n >> t >> k;
vector<ll> a(k);
for(int i = 0; i < k; ++i) cin >> a[i];
priority_queue<Node, vector<Node>, compare> pq;
for(int i = 1; i <= 2e6; ++i){
pq.push(Node(t * i + a[0], 0, i));
}
ll ans = -t * n;
while(n > 0){
Node cur = pq.top(); pq.pop();
ll cnt = get_amount(cur.d);
ll diff = min(n, cnt);
n -= diff;
ans += cur.cost * diff;
cur.h++;
if (cur.h < k){
cur.cost = t * cur.d + a[cur.h];
pq.push(cur);
}
}
cout << ans << "\n";
}
int main(void){
ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
clock_t cock = clock();
solve();
cerr << "Time elapsed: " << clock() - cock << "ms!\n";
return 0;
}
