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

while true {
    C -= B
    if C <= 0 {
        break
    }
    
    A -= D
    if A <= 0 {
        break
    }
}

print(A <= 0 ? "No" : "Yes")
