#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef set<int> si;
const int inf = 1e9;
const int mod = 1e9+7;

main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  int x, y, n;
  int a, b;
  cin >> x >> y >> n >> a;
  FOR(i, 1, n){
    b = a;
    cin >> a;
    if(b*y > a*x){
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
  return 0;
}