#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <map>
#include <functional>
#include <set>
#include <numeric>
#include <stack>
#include <utility>
#include <time.h>
//#include "util.h"

using namespace std;
typedef long long lint;
typedef unsigned long long ull;
typedef pair<lint, lint> Pii;

#define PI 3.14159265358979323846
#define EPS 1e-6
#define MOD ((lint)1000000007)
#define MIN(a,b) ((a)<(b)?(a):(b))
#define MAX(a,b) ((a)>(b)?(a):(b))
#define CHAR_BIT 8

template <typename _Ty>
ostream& operator << (ostream& ostr, const vector<_Ty>& v) {
	if (v.empty()) {
		cout << "{ }";
		return ostr;
	}
	cout << "{" << v.front();
	for (auto itr = ++v.begin(); itr != v.end(); itr++) {
		cout << ", " << *itr;
	}
	cout << "}";
	return ostr;
}

int main()
{
	//clock_t start, end;
	//start = clock();
	
	int X, Y, N, A0 = 0, A1;
	bool flag = true;
	cin >> X >> Y >> N;
	for (int i = 0; i < N; i++) {
		cin >> A1;
		if (X * A1 < Y * A0)
			flag = false;
		A0 = A1;
	}
	cout << (flag ? "YES" : "NO") << endl;

	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}