#include <iostream>
#include <vector>

using namespace std;

int main() {
	int x, y, n;
	cin >> x >> y >> n;

	vector<int> a(n, 0);
	for (int i = 0; i < n; i++) {
		cin >> a[i];
	}


	bool ok = true;
	for (int i = 1; i < n - 1; i++) {
		if (y * a[i] > x * a[i + 1]) {
			ok = false;
			break;
		}
	}

	cout << (ok ? "YES" : "NO") << endl;
	return 0;
}