def func():
    return

# n = int(input())
# s = input()
a, b, c, d = map(int, input().split())
# a = list(map(int, input().split()))
# a = input().split()

while True:
    c -= b
    if c <= 0:
        ans = "Yes"
        break

    a -= d
    if a <= 0:
        ans = "No"
        break

print(ans)