import strutils, sequtils, algorithm, future, math

{.warning[SmallLshouldNotBeUsed]: off.}

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

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