// Battle

func main() {
    let abcd = readLine()!.split(separator: " ").map{Int($0)!}
    var a = abcd[0]
    let b = abcd[1]
    var c = abcd[2]
    let d = abcd[3]

    while true {
        // 高橋くんの攻撃
        c -= b
        if c <= 0 {
            print("Yes")
            return
        }

        // 青木くんの攻撃
        a -= d
        if a <= 0 {
            print("No")
            return
        }
    }
}

main()