H,W,N,K = map(int,input().split())
masu_sum = H * W
flag = True
while True:
    if flag == False:
        break
    for i in range(1,N+1):
        masu_sum -= 1
        if masu_sum == 0:
            flag = False
            break
if i == K:
    print("YES")
else:
    print("NO")