#include <stdio.h>
#include <algorithm>
#include <vector>
#include <deque>
#include <string>
#include <iostream>
using namespace std;
using ll = long long;

void solve();
int main() {
	solve();
#ifdef DBG
	while (true);
#endif
}

//512
void solve() {
	int x, y, n, A[80];
	scanf("%d %d %d", &x, &y, &n);
	for (int i = 0; i < n; i++)
		scanf("%d", A + i);
	bool lost = false;
	for (int i = 0; i < (n - 1); i++)
		if (A[i + 1] < (A[i] * y + x - 1) / x)
			lost = true;
	printf("%s\n", lost ? "NO" : "YES");
}