#!/usr/bin/env perl

use strict;
use warnings;

my ($x, $y) = split / /,<>; chomp $y;
my $n = <>; chomp $n;
my @arr = split/ /,<>; chomp $arr[@arr - 1];
unshift @arr, 0;
$n++;
for (my $i = 0; $i < $n - 1; $i++) {
  if ($arr[$i] * $y > $arr[$i + 1] * $x) {
    print "NO\n";
    exit;
  }
}
print "YES\n";