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