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

int main()
{
	int x, y, n; cin>>x>>y>>n;
	vector<long> a(n);
	for(auto& e: a) cin>>e;
	for(int i=0; i+1<size(a); ++i)
		if (a[i]*y>a[i+1]*x) return cout<<"NO\n", 0;
	cout<<"YES\n";
}