#include <stdio.h>

int main(void){
  int a,b,c,d,win;
  scanf("%d %d %d %d",&a,&b,&c,&d);
  
  while(1){
    c -= b;
    if(c <= 0){
      win = 1;
      break;
    }
    a -= d;
    if(a <= 0){
      win = 0;
      break;
    }
  }
  
  swich (win){
    case 1 : puts("Yes"); break;
    case 0 : puts("No"); break;
  }
  
  return 0;
}