#include<iostream>
#include<fstream>
#include<string>
#include<cstring>
#include<stdio.h>
#include<algorithm>
#include<functional>
#include<vector>
#include<set>
#include<queue>
#include<list>
#include<stdio.h>
#include<stdlib.h>
#include<map>
#include<cstdio>
#include <iomanip>


using namespace std;


template<class T>bool chmax(T &a, const T &b) { return (a<b) ? (a = b, 1) : 0; }
template<class T>bool chmin(T &a, const T &b) { return (b<a) ? (a = b, 1) : 0; }

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

typedef int _loop_int;
#define rep(i,n) for(_loop_int i=0;i<(_loop_int)(n);++i)
#define FOR(i,a,b) for(_loop_int i=(_loop_int)(a);i<(_loop_int)(b);++i)
#define FORR(i,a,b) for(_loop_int i=(_loop_int)(b)-1;i>=(_loop_int)(a);--i)

#define DEBUG(x) cout<<#x<<": "<<x<<endl
#define DEBUG_VEC(v) cout<<#v<<":";REP(i,v.size())cout<<" "<<v[i];cout<<endl
#define ALL(a) (a).begin(),(a).end()

#define CHMIN(a,b) a=min((a),(b))
#define CHMAX(a,b) a=max((a),(b))

// mod
const ll MOD = 1000000007ll;
#define FIX(a) ((a)%MOD+MOD)%MOD

// floating
typedef double Real;
const Real EPS = 1e-11;
#define EQ0(x) (abs(x)<EPS)
#define EQ(a,b) (abs(a-b)<EPS)

typedef vector<int> vi;
typedef pair<int, int> pii;

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];
	}

	for (int i = 0; i < N - 1; i++) {
		if (A[i] * Y > A[i - 1]*X) {
			cout << "NO" << endl;
			return 0;
		}
	}

	cout << "YES" << endl;

	return 0;
}