#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
ll t, c[20002];
int main() {
ios_base::sync_with_stdio(false);
cin.tie(0); cout.tie(0);
ll n, k; cin >> n >> t >> k;
for (int i = 0; i < k; i++) {
cin >> c[i];
}
priority_queue<tuple<ll,ll,ll>> q;
ll r = 0, d = 1, t1, t2, t3, z;
q.push({-c[0], 4, 0});
while (n) {
tie(t1, t2, t3) = q.top(); q.pop();
z = min(n, t2); n -= z; r -= z * t1;
if (t3 + 1 < k) {
q.push({t1 - c[t3 + 1] + c[t3], t2, t3 + 1});
}
if (q.empty() || -c[0] - t * d > get<0>(q.top())) {
q.push({-c[0] - t * d, 4 * d + 4, 0}); d++;
}
}
cout << r << endl;
}
