import strutils, sequtils

let
  XY, N, A = stdin.readLine.split.map parseFloat
  (X, Y) = (XY[0], XY[1])

for i in 1 ..< A.len:
  let t = A[i] / Y
  if X * t < A[i - 1]:
    echo "NO"
    quit()

echo "YES"