1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
//#pragma GCC optimize("O3")
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
using namespace std;
namespace debug {
template <class c> struct rge { c b, e; };
template <class c> rge<c> range(c i, c j) { return rge<c>{i, j}; }
template <class c> char spk(...);
template <class c> auto spk(c *a) -> decltype(cerr << *a, 0);
struct stream {
  ~stream() { cerr << endl; }
  template <class c>
  typename enable_if<sizeof spk<c>(0) != 1, stream &>::type operator<<(c i) {
    cerr << boolalpha << i;
    return *this;
  }
  template <class c>
  typename enable_if<sizeof spk<c>(0) == 1, stream &>::type operator<<(c i) {
    return *this << range(begin(i), end(i));
  }
  template <class a, class b> stream &operator<<(pair<a, b> p) {
    return *this << "(" << p.first << ", " << p.second << ")";
  }
  template <class c> stream &operator<<(rge<c> d) {
    *this << "[";
    for (auto it = d.b; it != d.e; it++)
      *this << ", " + 2 * (it == d.b) << *it;
    return *this << "]";
  }
  stream &_dbg(const string &s, int i, int b) { return *this; }
  template <class c, class... cs>
  stream &_dbg(const string &s, int i, int b, c arg, cs... args) {
    if (i == (int)(s.size()))
      return (*this << ": " << arg);
    b += (s[i] == '(') + (s[i] == '[') + (s[i] == '{') - (s[i] == ')') -
         (s[i] == ']') - (s[i] == '}');
    return (s[i] == ',' && b == 0)
               ? (*this << ": " << arg << "     ")._dbg(s, i + 1, b, args...)
               : (s[i] == ' ' ? *this : *this << s[i])
                     ._dbg(s, i + 1, b, arg, args...);
  }
};
} // namespace debug
#ifdef DEBUG
#define dout debug::stream()
#define dbg(...) ((dout << "line:" << __LINE__ << " >> ")._dbg(#__VA_ARGS__, 0, 0, __VA_ARGS__))
#else
#define dout
#define dbg(...)
#endif
// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~



long long Solve(long long h, long long w, const vector<int> &d) {
  if (h == 0 || w == 0) return 0;
  if (w > h) swap(h, w);
  dbg(h, w);
  long long min_w_cover = 0;
  long long ww = w;
  long long big_d = -1;
  for (int i = 0; i < (int)d.size(); i++) {
    if (big_d == -1 && d[i] <= w) {
      big_d = d[i];
    }
    min_w_cover += ww / d[i] * big_d / d[i];
    ww %= d[i];
  }
  dbg(min_w_cover, big_d);
  return h / big_d * min_w_cover + Solve(h % big_d, w, d);
}


int main() {
  cin.tie(nullptr);
  ios_base::sync_with_stdio(false);
  int h, w, n;
  cin >> h >> w;
  cin >> n;
  vector<int> d(n);
  for (auto &x: d) cin >> x;
  if (h % d[0] != 0 || w % d[0] != 0) {
    cout << -1 << '\n';
    return 0;
  }
  reverse(d.begin(), d.end());
  cout << Solve(h, w, d) << '\n';
  return 0;
}