#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i = (a); i < (b); ++i)
#define REP(i,n) FOR(i,0,n)
#define SZ(n) (int)(n).size()
#define ALL(n) (n).begin(), (n).end()
#define MOD % 1000000007
using namespace std;
typedef long long LL;
typedef vector<int> VI;


int main() {
	int x, y, n;
	cin >> x >> y >> n;
	int a[101010];
	REP(i, n) {
		int ai;
		cin >> ai;
		a[i] = ai * 1000;
	}
	bool bo = true;
	REP(i, n - 1) {
		if (a[i] * y > a[i + 1] * x) bo = false;
	}
	cout << (bo ? "YES" : "NO") << endl;
	return 0;
}