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
#include <bits/stdc++.h>
#ifdef dbg
#define D(...) fprintf(stderr, __VA_ARGS__)
#define DD(...) D(#__VA_ARGS__ " = "), debug_helper::debug(__VA_ARGS__), D("\n")
#include "C:\Users\wsyear\Desktop\OI\templates\debug.hpp"
#else
#define D(...) ((void)0)
#define DD(...) ((void)0)
#endif
#define rep(i, j, k) for (int i = (j); i <= (k); ++i)
#define per(i, j, k) for (int i = (j); i >= (k); --i)
#define SZ(v) int((v).size())
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
using ll = long long;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;

using namespace std;

const int maxn = 110;

int h, w, n, a[maxn];

int main() {
  cin.tie(nullptr) -> ios::sync_with_stdio(false);
  cin >> h >> w >> n;
  rep (i, 1, n) cin >> a[i];
  if (h % a[1] != 0 || w % a[1] != 0) return cout << "-1\n", 0;
  ll ans = 1ll * (h / a[1]) * (w / a[1]);
  rep (i, 2, n) {
    ll delta = 1ll * (a[i] / a[i - 1]) * (a[i] / a[i - 1]) - 1;
    ans -= delta * (h / a[i]) * (w / a[i]);
  }
  cout << ans << '\n';
}