import Foundation

private func readInt() -> [Int]{
    return readLine()!.split(separator: " ").map{Int($0)!}
}

func mainB() {
    let line = readInt()
    var A = line[0]
    let B = line[1]
    var C = line[2]
    let D = line[3]
    
    while true {
        C -= B
        if C <= 0 {
            print("Yes")
            return
        }
        A -= D
        if A <= 0 {
            print("No")
            return
        }
    }
}

mainB()
