/* -*- coding: utf-8 -*-
 *
 * 512.cc: No.512 魔法少女の追いかけっこ - yukicoder
 */

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<string>
#include<vector>
#include<map>
#include<set>
#include<stack>
#include<list>
#include<queue>
#include<deque>
#include<algorithm>
#include<numeric>
#include<utility>
#include<complex>
#include<functional>
 
using namespace std;

/* constant */

const int MAX_N = 80;
const int INF = 1 << 30;

/* typedef */

/* global variables */

int as[MAX_N + 1];

/* subroutines */

/* main */

int main() {
  int x, y, n;
  scanf("%d%d%d", &x, &y, &n);

  for (int i = 0; i < n; i++) scanf("%d", &as[i]);
  as[n] = INF;

  bool ok = true;
  for (int i = 0; i < n; i++) {
    int b = (as[i] * y + (x - 1)) / x;
    if (b > as[i + 1]) {
      ok = false;
      break;
    }
  }

  if (ok) puts("YES");
  else puts("NO");
  return 0;
}