#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());
}
ll get_border(ll x){
return (x+1) * (x+1) - (x-1) * (x-1);
}
ll n, t, k;
vector<ll> a, b;
pair<ll, ll> calc(ll lambda){
int j = k;
pair<ll, ll> ans = make_pair(0, 0);
for(int i = 1; i < 2e6; ++i){
while(j > 0 && (t * (i-1) + a[j]) > lambda) j--;
if (j == 0) break;
ll amount = get_border(i);
ans.second += amount * j;
ans.first += amount * (b[j] + t * (i-1) * j);
}
return ans;
}
void solve(){
cin >> n >> t >> k;
a.resize(k+1);
for(int i = 1; i <= k; ++i) cin >> a[i];
b = a;
for(int i = 1; i<=k; ++i) b[i] += b[i-1];
ll l = 0, r = 2e12;
while(l < r){
ll mid = (l + r) >> 1;
pair<ll, ll> tmp = calc(mid);
if (tmp.second >= n) r = mid;
else l = mid + 1;
}
pair<ll, ll> tmp = calc(l);
tmp.first -= l * (tmp.second - n);
cout << tmp.first << "\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;
}
