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
#include <bits/stdc++.h>

using namespace std;

#define endl '\n'
#define L long long
#define MP make_pair
#define REP(i, n) for(int i = 0; i < n; ++i)
#define REPR(i, n) for(int i = n - 1; i >= 0; --i)
#define FOR(i, a, b) for(int i = a; i < b; ++i)
#define FORR(i, a, b) for(int i = b - 1; i >= a; --i)
#define EB emplace_back
#define ST first
#define ND second
#define S size
#define RS resize

template<class T> using P = pair<T, T>;
template<class T> using V = vector<T>;

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);

    L h, w;
    int n;
    cin >> h >> w >> n;

    V<L> d(n);
    REP(i, n) {
        cin >> d[i];
    }
    sort(d.begin(), d.end());

    if (h % d[0] != 0 || w % d[0] != 0) {
        cout << "-1\n";
        return 0;
    }

    L res = 0;
    L wp = 0, hp = 0;
    REPR(i, n) {
        L r = d[i];
        L wr = (w - wp) / r * r;
        L hr = (h - hp) / r * r;
        res += ((wp + wr) * (hp + hr) - wp * hp) / (r * r);
        wp += wr;
        hp += hr;
    }

    cout << res << '\n';
}