#include <cfloat>
#include <iostream>

using namespace std;

int main(int argc, const char* argv[])
{
	int X, Y, N;
	cin >> X >> Y >> N;
	int A[N];
	for (auto&& a : A) cin >> a;
	for (int i = 1; i < N; i++) {
		if (A[i] * X < A[i - 1] * Y) {
			cout << "NO" << endl;
			return 0;
		}
	}
	cout << "YES" << endl;
	return 0;
}