INT_MAX=10**11+7
MOD=10**9+7
def INPUT():return list(int(i) for i in input().split())
def LIST_1D_ARRAY(n):return [0 for _ in range(n)]
def LIST_2D_ARRAY(m,n):return [[0 for _ in range(n)]for _ in range(m)]
#=======================================================================
h1,s1,h2,s2=INPUT()
while(h1>0 and h2>0):
    h2-=s1
    if h2<=0:
        print("Yes")
        break
    h1-=s2
    if h1<=0:
        print("No")
        break
        
