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#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long int lld;
int d[50];
int n;
lld f(int a, int b)
{
	if(a==0 || b==0)return 0;
	if(a>b)swap(a,b);
	for(int i=n-1;i>=0;i--)
	{
		if(d[i]<=a)
		{
			lld x=f(a%d[i],b-b%d[i]);
			if(x==-1)return -1;
			lld y=f(a,b%d[i]);
			if(y==-1)return -1;
			return lld(a/d[i])*lld(b/d[i])+x+y;
		}
	}
	return -1;
}
int main()
{
	int a,b;
	scanf("%d %d",&a,&b);
	scanf("%d",&n);
	for(int i=0;i<n;i++)scanf("%d",&d[i]);
	printf("%lld\n",f(a,b));
}