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#include <bits/stdc++.h>

using namespace std;

#define ll long long

template<class T>
int ssize(T &c)
{
	return (int)c.size();
}

template<class T>
istream &operator>>(istream &is, vector<T> &vec)
{
	for (auto &v : vec)
		is >> v;

	return is;
}

template<class T>
auto operator<<(ostream &os, T &x)->decltype(x.end(), os);

template<class A, class B>
auto &operator<<(ostream &o, pair<A,B> &x)
{
	return o << "(" << x.first << " " << x.second << ")";
}

template<class T>
auto operator<<(ostream &os, T &x)->decltype(x.end(), os)
{
	os << "{";
	int i = 2;
	for(auto &e : x)
		os << (", ") + i << e, i = 0;

	return os << "}";
}

auto &operator<<(ostream &os, string &x)
{
	return os << x.c_str();
}

#ifdef DEBUG
#define LOG(x...) cerr << "["#x"]: ", [](auto... e){ ((cerr << e << "; "), ...) << "\n"; }(x)
#else
#define LOG(x...) 0
#endif

#define written_by return
#define efindus
#define in_2024 0

int main()
{
	cin.tie(NULL)->sync_with_stdio(false);

	int h, w;
	cin >> h >> w;
	if (h > w)
		swap(h, w);

	int n;
	cin >> n;

	vector<int> sizes_pre(n);
	cin >> sizes_pre;

	set<int> sizes(sizes_pre.begin(), sizes_pre.end());

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

	ll pre_res = 0, res = 0;

	int h_left = h, w_left = w, c_w = 0;

	while (h_left != 0 && w_left != 0) {
		int x = *(--sizes.upper_bound(min(h_left, w_left)));

		if (h_left == h)
			w_left -= x, c_w = x, pre_res = res;
		
		res += (c_w / x) * (h_left / x), h_left %= x;

		if (h_left == 0) {
			res += (w_left / c_w) * (res - pre_res), w_left %= c_w;
			if (w_left != 0)
				h_left = h;
		}
	}

	cout << res << "\n";

	written_by efindus in_2024;
}