#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
int z,l,n,c=1;
double d;
const int maxn=10000+2;
struct node
{
	int m,f;
};
node b[maxn];
char a[maxn];
int j=1,s;
char ss();
int max1;
using namespace std;
int main()
{
	//freopen("test.in","r",stdin);
	//freopen("test.out","w",stdout);
	freopen("sboost.in","r",stdin);
	freopen("sboost.out","w",stdout);
	
	cin>>l>>z>>n;
	d=z*1.0/l;
	max1=d;
	for(int i=1;i<=n;i++)
	{
		j*=2;
	}
	for(int i=1;i<=n;i++)
	{
		a[i]='0';
	}
	for(int i=1;i<=n;i++)
	{
		cin>>b[i].f>>b[i].m;
	}
	ss();
	cout<<max1<<endl;
	return 0;
}
char ss()
{
	for(int j=c;j<=n;j++)
	{
		a[j]='1';
		int h1=0,h2=0;
		for(int i=1;i<=n;i++)
		{
			if(a[i]=='1')
			{
				h1+=b[i].m;
				h2+=b[i].f;
				d=h1*1.0/h2;
				if(d>max1)
					max1=d;
			}
		}
		c++;
		ss();
		a[j]='0';
	}
	//if(c==n-1) return;
}