let input = readLine()!.split(separator: " ").map { Int($0)! }

let A = input[0]
let B = input[1]
let C = input[2]
let D = input[3]

let takahashi = C / B + (C % B > 0 ? 1 : 0)
let aoki = A / D + (A % D > 0 ? 1 : 0)
print(aoki >= takahashi ? "Yes" : "No")
