import Foundation

let inputs = readLine()!.components(separatedBy: " ").map{ Int($0)! }
let A = inputs[0]
let B = inputs[1]
let C = inputs[2]
let D = inputs[3]

var ARemain = A
var CRemain = C

for i in 1...100 {
    CRemain = CRemain - B
    
    if CRemain <= 0 {
        print("Yes")
        break
    }
    ARemain = ARemain - D
    
    if ARemain <= 0 {
        print("No")
        break
    }
    
}