#include <stdio.h>
int main(void){
  int a,b,c,d,i;
  scanf("%d",&a);
  scanf("%d",&b);
  scanf("%d",&c);
  scanf("%d",&d);
  for(i=0; i<100; i++){
    c = c-b;
    if(c <= 0){
      printf("Yes");
      break;
    }
    a = a-d;
    if(a <= 0){
      printf("No");
      break;
    }
  }
  return 0;
}