#include <iostream>
using namespace std;

struct iostream_init_struct
{ 
	iostream_init_struct()
	{
		std::cin.tie(0);
		std::cin.sync_with_stdio(false);
	}
} iostream_init;

int main()
{
	int X, Y;
	int N;
	cin >> X >> Y >> N;

	int A_previous = 0;
	for (int i = 0; i < N; ++i)
	{
		int A;
		cin >> A;
		if (A * X < A_previous * Y)
		{
			cout << "NO" << endl;
			return 0;
		}
		A_previous = A;
	}
	cout << "YES" << endl;
}