#include<stdio.h>

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