Imports System

Module practiceA
    Sub Main()
        Call test2()


    End Sub

    Sub test1()
        Dim S, W As Integer
        Dim arr(2) As String
        arr = Split(Console.ReadLine())
        S = arr(0)
        W = arr(1)

        If S > W Then
            Console.Write("safe")

        Else
            Console.Write("unsafe")
        End If

    End Sub

    Sub test2()
        Dim A, B, C, D, HP_A, HP_B As Integer
        Dim arr(4) As String
        arr = Split(Console.ReadLine())
        A = arr(0)
        B = arr(1)
        C = arr(2)
        D = arr(3)

        HP_B = C - B


        If HP_B <= 0 Then
            Console.Write("Yes")
            Exit Sub
        End If

        HP_A = A - D

        If HP_A <= 0 Then
            Console.Write("No")
            Exit Sub
        End If

        While True

            HP_B = HP_B - B

            If HP_B <= 0 Then
                Console.Write("Yes")
                Exit While
            End If

            HP_A = HP_A - D

            If HP_A <= 0 Then
                Console.Write("No")
                Exit While
            End If

        End While

    End Sub

End Module
