#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  int x, y;
  cin >> x >> y;
  int n;
  cin >> n;
  vector<int> a(n);
  REP (i, n) cin >> a[i];

  bool ck = true;
  REP (i, n-1)
    if (a[i] * y > a[i+1] * x)
      ck = false;

  if (ck)
    cout << "YES" << endl;
  else
    cout << "NO" << endl;
  
  return 0;
}