#include<stdio.h>
int main(){
  int a,b,c,d;
  int kai=1;
  
  scanf("%d %d %d %d",&a,&b,&c,&d);
  
  while(a>0&&c>0){
    if(kai%2==0){
      a=a-d;
    }
    else
      c=c-b;
  }
  if(a<=0)
    printf("No");
  else
    printf("Yes");
  
  return 0;
}