#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
using namespace std;

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

	int N; cin >> N;
	vector<int>A(N);
	for (int i = 0; i < N; i++)cin >> A[i];

	bool flag = true;
	for (int i = 0; i < N-1; i++) {
		if (A[i + 1]*X < A[i]*Y) {
			flag = false;
			break;
		}
	}

	cout << (flag ? "YES" : "NO") << endl;

    return 0;
}