#include<stdio.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)

int main(){
 int A,B, C, D;
 scanf("%d %d %d %d", &A, &B, &C, &D);
 int TAKAHASI = C/B;
 int AOKI = A/D;
 int TM = C % B;
 int AM = A % D;
 //printf("%d %d ",TAKAHASI, AOKI);
 if(TM > 0){
   TAKAHASI += 1;
 } 
 if(AM > 0){
   AOKI += 1;
 } 
 if (TAKAHASI <= AOKI){
   printf("Yes\n");
 }else {
   printf("No\n");
 }
 
  return 0;
}