open System

let No166 () =
    let IN = Console.ReadLine().Split(' ')
    let H, W, N, K = Int64.Parse IN.[0], Int64.Parse IN.[1], Int64.Parse IN.[2], Int64.Parse IN.[3]
    let mass = H * W
    if mass % N = K - 1L then
        printfn "NO"
    else 
        printfn "YES"

    ()

No166 ()