#include <CodeforcesSolutions.h>
#include <ONLINE_JUDGE <solution.cf(contestID = "1364",problemID = "A",method = "GET")>.h>
"""
    Author : thekushalghosh
    Team   : CodeDiggers
 
    I prefer Python language over the C++ language :p :D
        
    Visit my website : thekushalghosh.github.io
"""
import sys,math,cmath,time
start_time = time.time()
##########################################################################
################# ---- THE ACTUAL CODE STARTS BELOW ---- #################

def solve():
    a,b,c,d = invr()
    while True:
        a = a - d
        c = c - b
        if a <= 0:
            print("No")
        	break
        if c <= 0:
            print("Yes")
            break
            
################## ---- THE ACTUAL CODE ENDS ABOVE ---- ##################
##########################################################################
 
def main():
    global tt
    if not ONLINE_JUDGE:
        sys.stdin = open("input.txt","r")
        sys.stdout = open("output.txt","w")
    t = 1
    for tt in range(t):
        solve()
    if not ONLINE_JUDGE:
        print("Time Elapsed :",time.time() - start_time,"seconds")
        sys.stdout.close()
    
#---------------------- USER DEFINED INPUT FUNCTIONS ----------------------#
def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    return(input().strip())
def invr():
    return(map(int,input().split()))
 
#------------------ USER DEFINED PROGRAMMING FUNCTIONS ------------------#
def counter(a):
    q = [0] * max(a)
    for i in range(len(a)):
        q[a[i] - 1] = q[a[i] - 1] + 1
    return(q)
 
def string_counter(a):
    q = [0] * 26
    for i in range(len(a)):
        q[ord(a[i]) - 97] = q[ord(a[i]) - 97] + 1
    return(q)

def power_two(n):
    if n == 1:
        return(True)
    sttr = str(n)
    len_str = len(sttr)
    sttr = list(sttr)
    num = 0
    if (len_str == 1 and sttr[len_str - 1] == '1'): 
        return(False)
    while (len_str != 1 or sttr[len_str - 1] != '1'):
        if ((ord(sttr[len_str - 1]) - ord('0')) % 2 == 1):
            return(False)
        j = 0; 
        for i in range(len_str):  
            num = num * 10 + (ord(sttr[i]) - ord('0')); 
            if (num < 2): 
                if (i != 0):  
                    sttr[j] = '0'
                    j += 1
                continue
  
            sttr[j] = chr((num // 2) + ord('0'))
            j += 1; 
            num = (num) - (num // 2) * 2
        len_str = j
    return(True)

def getLeftmostBit(n): 
    m = 0
    while (n > 1) : 
        n = n >> 1
        m += 1
    return(m)
def getNextLeftmostBit(n, m) : 
    temp = 1 << m 
    while (n < temp) : 
        temp = temp >> 1
        m -= 1
    return m
def bitcounter(n) :
    m = getLeftmostBit(n) 
    return _countSetBits(n, m) 
def _countSetBits(n, m) :
    if (n == 0) : 
        return 0
    m = getNextLeftmostBit(n, m)
    if (n == (1 << (m + 1)) - 1) : 
        return ((m + 1) * (1 << m))
    n = n - (1 << m)
    return (n + 1) + bitcounter(n) + m * (1 << (m - 1)) 

def log_two(n): 
    return(math.log(n) / math.log(2))

#-----------------------------------------------------------------------#
        
ONLINE_JUDGE = __debug__
if ONLINE_JUDGE:
    input = sys.stdin.readline
    
main()


### FIXED CODE ###

#include <CodeforcesSolutions.h>
#include <ONLINE_JUDGE <solution.cf(contestID = "1364",problemID = "A",method = "GET")>.h>
"""
    Author : thekushalghosh
    Team   : CodeDiggers
 
    I prefer Python language over the C++ language :p :D
        
    Visit my website : thekushalghosh.github.io
"""
import sys,math,cmath,time
start_time = time.time()
##########################################################################
################# ---- THE ACTUAL CODE STARTS BELOW ---- #################

def solve():
    a,b,c,d = invr()
    while True:
        c = c - b
        if c <= 0:
            print("Yes")
            break
        a = a - d
        if a <= 0:
            print("No")
            break
            
################## ---- THE ACTUAL CODE ENDS ABOVE ---- ##################
##########################################################################
 
def main():
    global tt
    if not ONLINE_JUDGE:
        sys.stdin = open("input.txt","r")
        sys.stdout = open("output.txt","w")
    t = 1
    for tt in range(t):
        solve()
    if not ONLINE_JUDGE:
        print("Time Elapsed :",time.time() - start_time,"seconds")
        sys.stdout.close()
    
#---------------------- USER DEFINED INPUT FUNCTIONS ----------------------#
def inp():
    return(int(input()))
def inlt():
    return(list(map(int,input().split())))
def insr():
    return(input().strip())
def invr():
    return(map(int,input().split()))
 
#------------------ USER DEFINED PROGRAMMING FUNCTIONS ------------------#
def counter(a):
    q = [0] * max(a)
    for i in range(len(a)):
        q[a[i] - 1] = q[a[i] - 1] + 1
    return(q)
 
def string_counter(a):
    q = [0] * 26
    for i in range(len(a)):
        q[ord(a[i]) - 97] = q[ord(a[i]) - 97] + 1
    return(q)

def power_two(n):
    if n == 1:
        return(True)
    sttr = str(n)
    len_str = len(sttr)
    sttr = list(sttr)
    num = 0
    if (len_str == 1 and sttr[len_str - 1] == '1'): 
        return(False)
    while (len_str != 1 or sttr[len_str - 1] != '1'):
        if ((ord(sttr[len_str - 1]) - ord('0')) % 2 == 1):
            return(False)
        j = 0; 
        for i in range(len_str):  
            num = num * 10 + (ord(sttr[i]) - ord('0')); 
            if (num < 2): 
                if (i != 0):  
                    sttr[j] = '0'
                    j += 1
                continue
  
            sttr[j] = chr((num // 2) + ord('0'))
            j += 1; 
            num = (num) - (num // 2) * 2
        len_str = j
    return(True)

def getLeftmostBit(n): 
    m = 0
    while (n > 1) : 
        n = n >> 1
        m += 1
    return(m)
def getNextLeftmostBit(n, m) : 
    temp = 1 << m 
    while (n < temp) : 
        temp = temp >> 1
        m -= 1
    return m
def bitcounter(n) :
    m = getLeftmostBit(n) 
    return _countSetBits(n, m) 
def _countSetBits(n, m) :
    if (n == 0) : 
        return 0
    m = getNextLeftmostBit(n, m)
    if (n == (1 << (m + 1)) - 1) : 
        return ((m + 1) * (1 << m))
    n = n - (1 << m)
    return (n + 1) + bitcounter(n) + m * (1 << (m - 1)) 

def log_two(n): 
    return(math.log(n) / math.log(2))

#-----------------------------------------------------------------------#
        
ONLINE_JUDGE = __debug__
if ONLINE_JUDGE:
    input = sys.stdin.readline
    
main()