import strutils, sequtils, algorithm, future, math

{.warning[SmallLshouldNotBeUsed]: off.}

when isMainModule:
  var
    tmp = stdin.readline.split.map(parsefloat)
    (x, y) = (tmp[0] * 1000, tmp[1] * 1000)
    n = stdin.readline.parseint
    a = stdin.readline.split.map(parsefloat)

  for i in 0..<n-1:
    var
      t = a[i] / x
      d = t * y
    if d > a[i+1]:
      echo "NO"
      quit()
  echo "YES"