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#include <bits/stdc++.h>
using namespace std;

#define int long long
#define ll long long
#define ld long double
#define pb push_back
#define nd second
#define st first
#define sz size
#define forr(i, n) for(int i=1;i<=n;i++)
const ll infl=1e18+90;
const int inf=1e9+90;

vector<int> wek;

int fun(int a, int b)
{
    int ile=0;
    if(a==0||b==0) return 0;
    if(a>b) swap(a, b);
    for(auto it:wek)
    {
        if(a>=it)
        {
            ile+=(a/it)*(b/it);
            ile+=fun(a%it, b-b%it);
            ile+=fun(a-a%it, b%it);
            ile+=fun(a%it, b%it);
            return ile;
        }
    }
}

signed main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    int n, m;
    cin>>n>>m;
    int k;
    cin>>k;
    for(int i=1;i<=k;i++)
    {
        int a;
        cin>>a;
        wek.pb(a);
    }
    if(n%wek[0]!=0||m%wek[0]!=0)
    {
        cout<<"-1\n";
        return 0;
    }
    reverse(wek.begin(), wek.end());
    cout<<fun(n, m)<<"\n";
}